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Glossary

Computing has a habit of hiding simple ideas behind scary acronyms. Half the battle in this course is just vocabulary — so here is every new word in one place, in plain language. When a word shows up in class or on this site, it lands here.

0–9

Term What it means Where you met it
3-2-1 rule Three copies, on two kinds of storage, one in another place. Unit 4 · Backups
802.1Q tag The 4-byte sticker added to a frame after the source MAC, carrying the VLAN ID (IEEE, 1998) Unit 3 · VLANs

A

Term What it means Where you met it
AAAA record The DNS record that maps a name to an IPv6 address, the IPv6 version of an A record. Unit 3 · IPv6 in 55 minutes
Absolute path An address that starts at / and works from anywhere, like a full postal address. Unit 4 · Terminal survival and the directory tree
Absolute reference A reference pinned with $ (like \(L\)1) so it does not move when copied. Unit 7 · Office and collaborative tools
Accept / drop / reject A firewall rule's verdicts: "come in", silence (no answer at all), or "go away" with an ICMP error. Unit 3 · Lab 06-01 · The input chain
Access concentrator The provider's PPPoE server: the box every customer's router logs in to. Unit 3 · Lab 08-01 · PPPoE client
Access list (WiFi) The AP's ordered rules for which stations may join (by MAC, signal or time); first match wins. Unit 3 · Lab 05-05 · Snooper, registration table and access list
Access point Lets wireless devices join a wired LAN over radio — a mailbox you can reach without a street. Unit 1 · Networks
Access port A switch port for one end device, in one VLAN, sending frames untagged. Unit 3 · VLANs
Access token The list of identities and rights a program carries; an administrator gets two key rings, a standard one and an administrator one. Unit 5 · Users and groups on Windows
Account policy The rules the system enforces on accounts: when they expire, when they lock. Unit 5 · Account and password policies
ACE Access control entry: one line of an ACL, saying who, which permission, and Allow or Deny. Unit 5 · NTFS permissions
ACL Access control list: extra lines on a file's card for named users or groups (setfacl, getfacl); on Windows every file has one. Unit 5 · Special permissions and ACL
Activation How Windows checks that a copy has a valid licence. Without it: a notice on the desktop and some settings locked. Unit 2 · Installing Windows 11
Active Directory (AD) Microsoft's directory service (2000): DNS, Kerberos and LDAP in one product. Unit 6 · Domains and directory services
Add ARP For Leases A DHCP server option that writes the ARP entry for every lease it grants: the key and the name on the list at once. Unit 3 · Lab 02-03 · Static ARP
Add src to address list A firewall action that writes the packet's source address into an address list, optionally for a timeout. Unit 3 · Lab 06-03 · Address lists
Address classes The old A/B/C rule that fixed the border by the first number; replaced by CIDR. Unit 3 · Subnetting
Address list A named set of addresses (IPs, ranges, subnets) that one firewall rule can use at once: the bouncer's guest list. Unit 3 · Lab 06-03 · Address lists
adduser Debian's friendly tool for a new user: account, own group, private home. Unit 5 · Users and groups on Linux
Administrative distance How much a router trusts a route's source (connected 0, static 1); between equally specific routes, lower wins. Unit 3 · Lab 04-01 · The default route
Administrator (built-in) The all-powerful Windows account (SID ending in -500), left disabled by setup; not the same as the group Administrators. Unit 5 · Users and groups on Windows
Administrators The Windows group with power, the cousin of the Linux group sudo. Unit 5 · Users and groups on Windows
age A small modern tool to encrypt files, here with a passphrase. Unit 4 · Compression, encryption, integrity
Ageing A switch forgets a MAC after 300 s without traffic. Unit 3 · Ethernet, MAC addresses and switching
Alias A nickname for a cmdlet: in Windows PowerShell ls really runs Get-ChildItem. Unit 5 · PowerShell first contact
Allocation What a VM's disk file really takes on the host right now — usually far less than its capacity. Unit 2 · Three installs compared
Allowed addresses The inner addresses that live behind a WireGuard peer: which postcards belong in its envelope. Unit 3 · VPN with WireGuard
ALU Arithmetic Logic Unit — the CPU's hands: the part that actually computes (add, subtract, compare, AND, OR...). Unit 1 · Hardware
amd64 / x86_64 Two names for the 64-bit PC architecture, used by both AMD and Intel. Unit 2 · Planning an installation
ap-bridge The legacy RouterOS wireless mode for a normal access point that many clients can join. Unit 3 · Lab 05-03 · Your own access point
App password A separate password a mail provider like Gmail makes you create for a device, instead of your normal one. Unit 3 · Lab 09-01 · E-mail from the router
Application software Programs that do a job for the user: a browser, a game, WhatsApp. Unit 2 · What is an OS?
apt The package manager of Debian and Ubuntu: it places the orders with the repository and remembers every file it installs. Unit 2 · Package managers
Architecture (CPU)** The instruction set a CPU understands: amd64 (= x86_64) or arm64. Unit 2 · Planning an installation
Argument The part of a command line that says what the command works on: the /etc in ls -l /etc. Unit 4 · Terminal survival and the directory tree
arm64 The CPU architecture of phones and recent Macs; amd64 systems do not run on it. Unit 2 · Planning an installation
ARP Asks the network "which MAC has this IP?": shouting in the stairwell, answered by the door. Unit 3 · Ethernet, MAC addresses and switching
ARP cache (neighbour table) Where a host remembers the IP → MAC answers for a while; ip neigh shows it. Unit 3 · Ethernet, MAC addresses and switching
ASCII American Standard Code for Information Interchange — the codebook that maps one byte to one character: 0100 1000 = 72 = "H". Unit 1 · Data
Asymmetric path A conversation whose packets go out by one route and come back by another. Unit 3 · Lab 08-03 · PPTP and SSTP
Authoritative server The DNS server that holds the real records of a domain. Unit 3 · DHCP and DNS
Auto MDI-X Ports that detect the cable and swap pairs by themselves, so crossovers are no longer needed. Unit 3 · Cabling a LAN
Availability The data or service is there when you need it. Unit 6 · Why protect systems
Available (memory) The memory programs could still get, counting the cache Linux hands back on demand: the honest number in free -h. Unit 5 · Monitoring performance
Available from A RouterOS service setting listing who may connect: a door that only opens for people already in the garden. Unit 3 · Lab 01-05 · Secure your router

B

Term What it means Where you met it
Backbone A shared network in the middle that joins several LANs' routers. Unit 3 · Routing
Backdoor A hidden program that lets attackers into a computer (Linux Mint, 2016) Unit 2 · Verify an ISO
Background (job) A command started with &: it runs while the terminal stays free for you. Unit 5 · Processes
Backup A copy from another moment, in another place, that you have already tried to restore. Unit 4 · RAID is not a backup
Band A range of radio frequencies Wi-Fi may use: 2.4, 5 or 6 GHz. Unit 3 · Wireless LAN
Bandwidth test RouterOS's treadmill stress test: how much can this link carry at most? Unit 3 · Lab 09-03 · The toolbox
Base clock The speed a CPU can hold forever under load. Unit 1 · CPU
Baseline Measurements of a machine when nothing is wrong, so the numbers under load mean something. Unit 5 · Monitoring performance
bash The command-line shell of most Linux systems. Unit 2 · OS architecture
Batch file A .bat file of Windows commands: the cousin of a shell script. Unit 4 · Scheduling tasks
Beacon The "here I am" message an access point broadcasts about ten times per second, carrying its SSID. Unit 3 · Lab 05-02 · Connect list
Binary The machine's number system: only two digits, 0 and 1. Two states are impossible to confuse, so binary is cheap and reliable. Unit 1 · Data
Binary (program)** The translated program the CPU runs and no person can read: the dish. Unit 2 · Software licences
Binary backup A .backup file: a save file of the whole configuration, users included, for restoring the same router. Unit 3 · Lab 01-06 · Backup, reset and restore
Bind mount A folder of the server you choose, shown inside a container so its files survive the box. Unit 6 · Images, volumes and ports
BIOS Basic Input/Output System — the old PC firmware (IBM PC, 1981), replaced by UEFI. People still say "the BIOS" out of habit. Unit 1 · Boot
Bit Binary digit — the smallest unit of information: one yes/no question, a 1 or a 0. Unit 1 · Data
Block The fixed-size piece (usually 4 KiB) a file system hands out; even a 6-byte file takes a whole one. Unit 4 · Terminal survival and the directory tree
Block size The number of addresses in one subnet, 2 to the power of the host bits; subnets start at its multiples. Unit 3 · Subnetting
Bluetooth Short-range wireless interface for peripherals (headphones, mice, watches). Devices must be paired once. Named after a Viking king who united tribes. Unit 1 · Peripherals
Boost clock The top speed a CPU can sprint to for a while, as long as it stays cool enough. Unit 1 · CPU
Boot / booting Starting a computer: the relay from power button to login (PSU → firmware → POST → bootloader → kernel). From "pulling yourself up by your bootstraps". Unit 1 · Boot
Boot order The firmware's list of devices to try, in order, when looking for a bootloader. Unit 2 · Verify an ISO
Bootable USB A USB stick with an installation image written onto the whole device, so the firmware can start from it. Unit 2 · Verify an ISO
Bootloader Small program that finds the OS kernel on the disk, loads it into RAM and hands it the CPU. GRUB on Linux, Windows Boot Manager on Windows. Unit 1 · Boot
BOOTP The network boot request a router in Netinstall mode sends: "who can give me a system?" Unit 3 · Lab 01-07 · Reinstall RouterOS with Netinstall
Bottleneck The slowest resource (CPU, memory, disk or network), which sets the pace of the whole kitchen. Unit 5 · Monitoring performance
Brace expansion {01..12}: the shell generates text whether files exist or not. Unit 5 · Back to the shell
Branch A separate line of commits that grows apart from main: a draft page you glue into the album when it is good. Unit 7 · Git remotes and collaboration
Branding package A special RouterOS package (.dpk) that changes the logo, name, URLs and default configuration a router shows. Unit 3 · Lab 01-04 · Your own brand
Bridge A software switch inside the router: the corridor that joins separate ports (rooms) into one LAN. Unit 3 · Wired LAN with RouterOS
Bridge port An interface handed over to a bridge (RouterOS says slave); configure the bridge, never its ports. Unit 3 · Lab 02-01 · DHCP server
Broadcast A message "to everybody on this network"; MAC ff:ff:ff:ff:ff:ff, a leaflet in every letterbox. Unit 3 · Ethernet, MAC addresses and switching
Broadcast address Host bits all 1: "to everybody in this network", never given to a machine. Unit 3 · IPv4 addressing
Broadcast domain The set of devices that hear each other's broadcasts; one per VLAN. Unit 3 · VLANs
BSSID The MAC address of one access point's radio; one SSID can have many BSSIDs. Unit 3 · Wireless LAN
Btrfs A Linux file system that never overwrites in place, so it can take instant snapshots. Unit 4 · File systems
Build Producing the final format (the PDF) from the sources with a command, the same way every time. Unit 7 · Docs as code
Builtin A command that lives inside Bash itself (cd, history); documented with help, not man. Unit 5 · Back to the shell
Burst Lets a queue go above its max-limit for a while, as long as its recent average speed stays low. Unit 3 · Lab 07-04 · Burst
Burst-limit The top speed a queue allows during a burst. Unit 3 · Lab 07-04 · Burst
Burst-threshold The average speed that switches a burst off above it, and back on below it. Unit 3 · Lab 07-04 · Burst
Burst-time The window the burst average is calculated over; not how long the burst lasts. Unit 3 · Lab 07-04 · Burst
Bus The shared set of wires connecting CPU, memory and I/O — the corridor everything travels through. Carries data, addresses and control signals. Unit 1 · Hardware
Byte 8 bits together. 2⁸ = 256 possible values — enough for one ASCII character. Unit 1 · Data
Bytecode What the Java compiler produces: instructions for the imaginary JVM instead of a real CPU. Unit 5 · What a development machine needs

C

Term What it means Where you met it
CA Certificate authority: an organisation your browser trusts to vouch for whose key a certificate holds. Unit 3 · SSH and TLS
Cable tester Two boxes that check each wire of a cable, one light per pin. Unit 3 · Cabling a LAN
Cache Small, ultra-fast memory built next to the CPU. It keeps copies of what RAM was recently asked for, so the CPU waits less. Unit 1 · CPU
Cache hit / miss Hit: the CPU finds what it needs in cache (fast). Miss: it has to wait for RAM. Unit 1 · CPU
Capacity The size of a virtual disk as the guest sees it (25, 20 or 64 GiB in the lab). Unit 2 · Three installs compared
Captive portal The login page a hotel or airport Wi-Fi shows before it lets you on the Internet. Unit 3 · Lab 02-02 · Static DHCP leases
Case-sensitive Capitals count: on Linux Documents and documents are two different names. Unit 4 · Terminal survival and the directory tree
CC / BCC Carbon copy (people who should know); blind carbon copy (the other recipients cannot see these addresses) Unit 7 · Email and messaging
Cell One square of a spreadsheet, with an address like B3. Unit 7 · Office and collaborative tools
Certificate The digital ID card a website shows your browser. A lab server signs its own, so the browser warns that nobody vouches for it. Unit 2 · Proxmox VE
CGNAT Carrier-Grade NAT: your provider adds a second NAT in front of yours (range 100.64.0.0/10) Unit 3 · NAT and Internet access
chage Sets ageing and expiry: -E ends the account, -M ages the password, -d 0 forces a change. Unit 5 · Account and password policies
Chain A group of firewall rules for one kind of traffic: input (to the router), forward (through it), output (from it). Unit 3 · Lab 06-01 · The input chain
Channel The slice of a band one access point uses; at 2.4 GHz only 1, 6 and 11 do not overlap. Unit 3 · Wireless LAN
Channel width How many MHz a channel uses (20, 40, 80 or 160): wider is faster but leaves room for fewer networks. Unit 3 · Lab 05-01 · Wireless basics and your radio name
Cheat sheet A one-page summary of the commands you forget, task first, each with a real example. Unit 5 · Sysadmin cheat sheet
check-gateway A route option that pings its gateway every 10 seconds and switches the route off after two timeouts. Unit 3 · Lab 04-01 · The default route
Checksum A short fingerprint computed from every byte of a file; one changed bit gives another fingerprint. Unit 4 · Compression, encryption, integrity
Checksum / hash A short fingerprint of a file; one changed byte gives a completely different one. Unit 2 · Verify an ISO
chgrp Changes only a file's group, to a group the owner belongs to. Unit 5 · Linux permissions
Chipset The motherboard's reception desk: a chip that manages the slower connections (USB, SATA, audio, network) and links them to the CPU. Unit 1 · Motherboard
chmod Changes permissions, in symbolic (u+x) or octal (640) notation. Unit 5 · Linux permissions
chown Changes a file's owner (and group); only root may give files to another user. Unit 5 · Linux permissions
CHR Cloud Hosted Router: RouterOS in a virtual machine. Unit 3 · Meet RouterOS
CIA triad Confidentiality, integrity, availability: the three things security protects. Unit 6 · Why protect systems
CIDR The /prefix notation (1993) that replaced address classes. Unit 3 · IPv4 addressing
ClamAV A free antivirus that compares files with signatures of known malware. Unit 6 · Basic security utilities
Class server The rented machine in a data centre that hosts every student's VMs this course: the host. Your PC only shows the screen. Unit 2 · Virtualisation
Classifier The field PCQ splits traffic by (source or destination address): one sub-stream for each value. Unit 3 · Lab 07-05 · PCQ
CLI Command-Line Interface: typing commands, as in bash. Unit 2 · OS architecture
Client The program that asks for a service: the customer at the restaurant hatch. Unit 6 · Clients, servers and shared resources
Client isolation WiFi clients reach the Internet but not each other, like café Wi-Fi; on RouterOS, Default Forward off. Unit 3 · Lab 05-05 · Snooper, registration table and access list
Clock The CPU's heartbeat: a signal ticking at a fixed rate, measured in hertz (GHz = billions of ticks per second). Unit 1 · CPU
Cluster Several hypervisor nodes managed together from one page. Unit 2 · Proxmox VE
CMD The old Windows command prompt from the 1980s; not the same as PowerShell. Unit 5 · PowerShell first contact
Cmdlet A PowerShell command named Verb-Noun (Get-Process, Stop-Service): long, but you can guess it. Unit 5 · PowerShell first contact
CMOS battery The coin cell on the motherboard (usually a CR2032) that keeps the clock and firmware settings alive when unplugged. Unit 1 · Motherboard
CN Common name: the name written inside a certificate. Unit 3 · SSH and TLS
Collision domain The devices that could talk on top of each other on a shared cable; a bridge or switch splits it, one per port. Unit 3 · Lab 03-01 · Bridge
Command substitution $(...): run a command and keep what it prints. Unit 4 · Shell scripts
Comment Text after # that the shell ignores; it is for humans. Unit 4 · Shell scripts
Commit A photo in the album: a snapshot of the whole project with a message, author, date and identifier. Unit 7 · Git basics
Community (SNMP) The shared word an SNMP manager must know to read a device, sent in clear text in v1/v2c: the library card. Unit 3 · Lab 09-05 · SNMP
Compiler The cook who turns a recipe (source code) into something the machine can run; for Java, javac. Unit 5 · What a development machine needs
Compose file compose.yaml: the loading plan that describes every service of an application in one file. Unit 6 · Composing services
Compression Writing the same information in fewer bytes by describing repetition: vacuum-packing the jumper. Unit 4 · Compression, encryption, integrity
Computer account The account a joined computer gets in the directory, its name ending in $. Unit 6 · Joining a domain
Confidentiality Only the right people can read the data. Unit 6 · Why protect systems
Configure script Your own .rsc handed to Netinstall that replaces the default configuration and runs on the first boot. Unit 3 · Lab 01-07 · Reinstall RouterOS with Netinstall
Conflict markers The <<<<<<<, ======= and >>>>>>> lines that wrap your version and theirs in a conflicted file. Unit 7 · Git remotes and collaboration
Connect list A station's ordered rules for which APs it may join (connect=yes/no); first match wins. Unit 3 · Lab 05-02 · Connect list
Connected route A route that appears by itself when the router gets an address in a network. Unit 3 · Routing
Connection state The stamp connection tracking puts on every packet: new, established, related or invalid. Unit 3 · Lab 06-08 · Connection tracking
Connection tracking The router's memory of every conversation crossing it, used by NAT and the firewall. Unit 3 · Ports and firewalls
Consent prompt The Yes / No UAC prompt shown to members of Administrators. Unit 5 · Users and groups on Windows
Constraint A limit (law, budget, hardware, skills, imposed platform) that removes candidates before any comparison — the allergy. Unit 7 · Software needs in real workplaces
Container A closed room inside a host's system with its own files, programs and users, but no kernel of its own: it borrows the host's. Unit 2 · Proxmox VE
Containerfile The text recipe of an image (FROM, COPY, RUN, EXPOSE, CMD); Docker calls it Dockerfile. Unit 6 · Images, volumes and ports
containerlab A tool that starts small Linux machines and routers as containers and cables them from a text file. Unit 3 · How a message travels
Control What you do to lower a risk. Unit 6 · Why protect systems
Copyleft Share alike: changed versions you distribute must keep the same free licence and their source (GPL) Unit 2 · Software licences
Copy-on-write Writing changes to new blocks instead of over the old ones; what makes Btrfs snapshots instant. Unit 4 · File systems
Copyright The author's automatic rights over their work; nobody may copy it without permission. Unit 2 · Software licences
Core A complete processing unit (CU + ALU + registers) inside the CPU chip: one more chef in the kitchen. Unit 1 · CPU
CPU Central Processing Unit — the chef: the part that actually runs the program, one fetch–decode–execute loop at a time. Unit 1 · Hardware
Create mask The permissions Samba allows on new files of a share (0660 = the group can write) Unit 6 · Share permissions and groups
Creative Commons Family of licences for text and creative works (e.g. CC BY-SA 4.0), not recommended for software. Unit 7 · Software by licence and purpose
Credential prompt The UAC prompt that asks a standard user for an administrator's name and password. Unit 5 · Users and groups on Windows
cron The Unix daemon that runs commands at scheduled times: the alarm clock. Unit 4 · Scheduling tasks
Crontab A user's table of cron tasks: five time fields and a command per line. Unit 4 · Scheduling tasks
CSV Comma-Separated Values: a plain-text table, values only, that Git can diff line by line. Unit 7 · Office and collaborative tools
CU Control Unit — the chef's head: fetches the next instruction, decodes it, and orders the other parts around. Lives inside the CPU. Unit 1 · Hardware
CUPS The print spooler of Linux and macOS; speaks IPP on port 631. Unit 6 · Print server

D

Term What it means Where you met it
Daemon A program that runs in the background, without a window, waiting for something. Unit 4 · Scheduling tasks
Data Raw symbols with no meaning yet: a 0, a letter, a number. Meaning is added by us, never by the machine. Unit 1 · Data
dBm Signal strength in decibels relative to 1 mW; negative, closer to zero is stronger, −3 dB is half. Unit 3 · Wireless LAN
DDR Double Data Rate — RAM that transfers data twice per clock tick. "DDR4-3200" = 3,200 million transfers per second. Unit 1 · Memory
Debian Free operating system made by volunteers since 1993; Debian 13 "trixie" runs deb-lab, and Ubuntu is built from it. Unit 2 · Installing Debian
Deduplication Storing each identical piece of data only once and noting "same as before" elsewhere. Unit 4 · restic and the restore drill
Default ACL ACL lines on a folder that every new file created inside copies automatically. Unit 5 · Special permissions and ACL
Default Authenticate Whether an AP (or station) lets in someone that no access-list (or connect-list) rule mentions. Unit 3 · Lab 05-02 · Connect list
Default configuration A new MikroTik's setup: ether1 WAN, the rest a LAN bridge at 192.168.88.1 with a DHCP server. Unit 3 · Meet RouterOS
Default Forward Whether clients of the same AP may talk to each other; off means client isolation. Unit 3 · Lab 05-05 · Snooper, registration table and access list
Default gateway The router's address inside my own network: the post office for every letter not for a neighbour. Unit 3 · Configuring TCP/IP on hosts
Default route The route to 0.0.0.0/0, "all other directions": used only when no more specific route matches. Unit 3 · Lab 04-01 · The default route
Defence in depth Several controls in layers, so that if one fails the next still stands. Unit 6 · Why protect systems
Defragmentation Moving the pieces of files on a hard disk back together so the head travels less; never for SSDs. Unit 5 · Maintenance and optimisation
Degraded A RAID array missing a disk: it still works, and the next failure is the last. Unit 4 · LVM and RAID
Deny by default A firewall list of the form "nobody enters except...": whatever you forget stays closed. Unit 6 · Basic security utilities
Dependency A package that another package needs in order to work; apt adds it to the order by itself. Unit 2 · Package managers
Development software Tools to build other software: Git, editors, compilers — the knives and moulds. Unit 7 · Software by licence and purpose
/dev/null The bin of Linux: anything sent there disappears. Unit 5 · Back to the shell
df Disk free: how full each mounted file system is — reads the sign on the pantry door. Unit 4 · Mounting file systems
DFS Dynamic Frequency Selection: on radar channels of 5 GHz the AP listens first and leaves if it hears a radar. Unit 3 · Lab 05-01 · Wireless basics and your radio name
DHCP The town hall desk that lends a newcomer an address plus mask, gateway and DNS. Unit 3 · DHCP and DNS
DHCP client The side that asks for IP settings; your phone is one every time it joins a WiFi. Unit 3 · Lab 01-02 · Internet access through the class AP
DHCP network The part of a RouterOS DHCP server that says what reception tells every guest: gateway, DNS, mask. Unit 3 · Lab 02-01 · DHCP server
DHCP option Extra information sent with a lease, each with a number: 43 tells an AP where its controller is. Unit 3 · Lab 02-02 · Static DHCP leases
DHCP pool The range of addresses a DHCP server may hand out automatically, e.g. 10.G.0.100–199. Unit 3 · Wired LAN with RouterOS
DHCP Setup RouterOS's wizard that builds a whole DHCP server (pool, network, server) from a few questions. Unit 3 · Lab 02-01 · DHCP server
Differential backup A copy of what changed since the last full backup: "everything since Sunday", rewritten each night. Unit 4 · Backups
dig A command that asks a DNS server a question and prints the answer. Unit 3 · DHCP and DNS
Digital signature Proof of who published a file, made with a key only the maker holds. Unit 2 · Verify an ISO
DIMM The long RAM module used in desktops and servers. Unit 1 · Memory
Direct delivery Sending straight to a host in your own network, without a gateway. Unit 3 · Routing
Directory The central database of users, groups and computers, arranged in a tree. Unit 6 · Domains and directory services
Disk The pantry (HDD or SSD): huge, much slower than RAM, and non-volatile — your files survive power cuts. Unit 1 · Hardware
Disk Management The graphical Windows tool to initialize disks and create, shrink and re-letter volumes. Unit 4 · Windows Disk Management
diskpart The Windows command-line tool for disks, partitions and volumes: the fdisk of Windows. Unit 4 · Windows Disk Management
Display filter A Wireshark expression (arp, ip.addr == …) that hides non-matching frames without deleting them. Unit 3 · Wireshark: first capture
DisplayPort VESA's computer-monitor video interface; it can also travel inside a USB-C cable. Unit 1 · Peripherals
Distinguished name (DN) The full path of an object in the directory, read right to left: CN=Marta Soler,OU=Dev,DC=tramuntana,DC=internal. Unit 6 · Domain users, groups and OUs
Distributed (version control) Every clone holds the complete history, so no single copy is "the real one". Unit 7 · Git remotes and collaboration
Distribution A complete OS built around the Linux kernel: Debian, Ubuntu, Fedora... Unit 2 · Comparing OSes
DNS The Domain Name System: a tree that turns names into addresses. Unit 3 · DHCP and DNS
DNS forwarder Where a DNS server sends the questions about names it does not own. Unit 6 · Domains and directory services
DNS record (A, AAAA, CNAME, MX, NS, PTR) One entry in a zone: IPv4, IPv6, alias, mail server, name servers, reverse. Unit 3 · DHCP and DNS
DNS server The machine a host asks to turn names into addresses: the address book. Unit 3 · Configuring TCP/IP on hosts
Docker The tool (2013) that made containers one command; uses a root daemon. Unit 6 · Containers
Docs as code Writing documentation like code: plain text, in Git, reviewed, and built by one command. Unit 7 · Docs as code
Domain Computers that trust one central server to know every user, group and computer and to check every password. Unit 6 · Domains and directory services
Domain account An account that lives on a company server rather than on the PC itself; it comes back in Unit 6. Unit 5 · Users and groups on Windows
Domain Admins The built-in group of the people who administer the domain. Unit 6 · Domain users, groups and OUs
Domain controller (DC) The server that holds the directory and answers the logins of the domain. Unit 6 · Domains and directory services
DORA DHCP's four messages: Discover, Offer, Request, Acknowledge. Unit 3 · DHCP and DNS
Dotted decimal Writing an IPv4 address as four decimal numbers with dots: 10.3.0.11. Unit 3 · IPv4 addressing
dpkg Debian's low-level package tool: installs one package file, but does not fetch what it depends on. Unit 2 · Package managers
DRAM Dynamic RAM — stores each bit in 1 transistor + 1 leaky capacitor, so it must be refreshed constantly. Cheap and dense: used for RAM. Unit 1 · Memory
Drive letter The name Windows gives a volume (C:, D:); it belongs to the volume, not the disk. Unit 4 · Windows Disk Management
Driver Program that lets the operating system use one specific device — the translator at the door between the OS and the hardware. Unit 1 · Peripherals
Dry run --dry-run: show what a command would do, without doing it. Unit 4 · Backups
dst-nat Destination NAT: changes where a packet goes, so the Internet can reach a server inside the LAN. Unit 3 · Lab 06-05 · Destination NAT
du Disk usage: adds up how much space one folder takes — goes in and weighs one box. Unit 4 · Mounting file systems
Dual boot Two OSes on one PC, choosing one at start-up; not virtualisation. Unit 2 · Virtualisation
Dual channel Two independent paths between the CPU and RAM, used at once: two modules in the right slots, double the bandwidth. Unit 1 · Memory
Dual stack A host running IPv4 and IPv6 at the same time, with two sets of addresses and two routing tables. Unit 3 · IPv6 in 55 minutes
Dynamic lease A lease created on the fly from the pool for a device the server has never seen (flag D). Unit 3 · Lab 02-02 · Static DHCP leases

E

Term What it means Where you met it
EAP (Enterprise) Wi-Fi security where every user has their own login, checked by a server, like eduroam. Unit 3 · Lab 05-03 · Your own access point
ECC Error-Correcting Code memory — RAM with extra bits that detect and fix single-bit errors. Common in servers. Unit 1 · Memory
ECMP Equal Cost Multi-Path: several routes to the same place with the same distance, all used at once. Unit 3 · Lab 04-04 · ECMP
EFI System Partition Small FAT32 partition where UEFI finds the bootloader. The glossary has an ESP row; extend its link instead of adding a new one. Unit 2 · Planning an installation
EICAR test file A harmless 68-character text every antivirus detects, made for testing. Unit 6 · Basic security utilities
Elevation prompt The UAC question asked before a program gets the administrator token. Unit 5 · Users and groups on Windows
Embedded system A computer hidden inside another machine doing one job: a router, a TV, a car. Unit 2 · Comparing OSes
Emulation Imitating a whole processor in software: works everywhere, slowly. Unit 2 · Virtualisation
Emulator A whole pretend device (e.g. an Android phone) running as a virtual machine inside your PC. Unit 5 · What a development machine needs
Encapsulation Each layer, going down, puts the data from above in its own envelope (header); decapsulation opens them going up. Unit 3 · How a message travels
Encryption Turning data into noise that only the key or passphrase turns back: the padlocked box. Unit 4 · Compression, encryption, integrity
End of support The day a maker stops sending security updates for a version. After it, new holes stay open for ever. Unit 2 · Software and updates on Windows
Endpoint A peer's real address and UDP port: where the outer envelope is sent. Unit 3 · VPN with WireGuard
Entropy The average surprise of a source (Shannon). Repetitive files have low entropy and compress well; random-looking files resist compression. Unit 1 · Data
Envelope MAIL FROM and RCPT TO: who hands the letter over and who gets it, separate from the From: line inside. Unit 7 · Email and messaging
Environment variable A named note a process carries and hands, as a copy, to the programs it starts; export puts it on the sheet. Unit 5 · Configuring the system by command
Environment variable (containers)** A NAME=value passed with -e that an image reads at start, such as a database password. Unit 6 · Images, volumes and ports
Ergonomics Adapting the workplace to the person: screen distance and height, chair, posture, breaks. Unit 1 · Health and safety
ESD Electrostatic discharge — a static-electricity spark. You feel it from ~3,000 V, but it can damage components below 100 V. Unit 1 · Health and safety
ESP EFI System Partition — small FAT32 partition where a UEFI machine keeps its bootloader files. Unit 1 · Boot
/etc/group The list of groups, their GIDs and their members. Unit 5 · Users and groups on Linux
/etc/passwd The list on the wall: who exists, with name, UID, GID, home and shell; everyone can read it, no passwords inside. Unit 5 · Users and groups on Linux
/etc/shadow The file with the password hashes and expiry dates; only root (and the group shadow) can read it. Unit 5 · Users and groups on Linux
EtherType The frame field that says what is inside: 0x0800 = IPv4, 0x0806 = ARP. Unit 3 · Ethernet, MAC addresses and switching
EULA End-User Licence Agreement: the text you accept with "I agree". Unit 2 · Software licences
Event ID Windows number for one kind of event, e.g. 4625 = failed logon; not a PID. Unit 5 · Logs and journald
Event Viewer Windows tool (eventvwr.msc) for reading the System, Application and Security event logs. Unit 5 · Logs and journald
exFAT Microsoft's file system for sticks and SD cards (2006): read by Windows and Linux, no 4 GiB file limit. Unit 4 · File systems
Exit code The number a command leaves when it ends, kept in $?: 0 is success, anything else is failure. Unit 4 · Shell scripts
Exit status Code systemd shows when a service ends, e.g. 203/EXEC; it says where it failed, the log says why. Unit 5 · The case of the failed service
/export RouterOS command that prints the whole configuration as the commands that rebuild it; readable text, not a backup. Unit 3 · Wired LAN with RouterOS
Export (NFS)** A directory the NFS server offers to certain machines, one line in /etc/exports. Unit 6 · NFS
Export (RouterOS) An .rsc text script of the configuration: readable, editable, for another router, but with no users. Unit 3 · Lab 01-06 · Backup, reset and restore
ext4 The default Linux file system of Debian and Ubuntu (2008), with a journal. Unit 4 · File systems
Extended partition On MBR, a primary entry turned into a container that holds logical partitions. Unit 4 · Partitions: MBR and GPT

F

Term What it means Where you met it
fail2ban Reads the logs and bans an IP after too many failed logins. Unit 6 · Basic security utilities
Failover Switching automatically to a backup path when the main one fails. Unit 3 · Lab 04-05 · Recursive routing and failover
Fast Forward (bridge) Fast Path for a bridge with exactly two ports; it even skips learning MAC addresses. Unit 3 · Lab 03-02 · Bridge performance
Fast Path RouterOS forwarding that skips the extra work of the Linux kernel when no feature needs to see the packets. Unit 3 · Lab 03-02 · Bridge performance
Fast-forward A pull where you had nothing new, so Git simply moves forward to the other person's commits. Unit 7 · Git remotes and collaboration
FastTrack Lets established and related connections skip most of the router's work: much faster, but they skip queues too. Unit 3 · Lab 06-08 · Connection tracking
FAT32 An old file system (1996) that almost every device reads; at most 4 GiB minus 1 byte per file. Unit 4 · File systems
Fetch–decode–execute The CPU's endless heartbeat: get the next instruction from RAM, understand it, do it. A 3 GHz CPU repeats it about 3 billion times per second. Unit 1 · Hardware
FHS Filesystem Hierarchy Standard: the rules for what goes in /etc, /usr, /var...; version 3.0 in 2015. Unit 4 · Terminal survival and the directory tree
FIB Forwarding Information Base: the fast table, built from the best active routes, that packets are really sent with. Unit 3 · Lab 04-04 · ECMP
Fibre optic Cable that carries bits as pulses of light in a glass thread: kilometres of reach, immune to electrical noise. Unit 1 · Networks
File descriptor The ticket number the kernel hands back for an open file. Unit 2 · OS architecture
File History The Windows tool that copies your folders to another drive and keeps old versions. Unit 4 · restic and the restore drill
File server A server that keeps one copy of the files for everybody: the filing cabinet in the corridor. Unit 6 · Samba file server
File system The OS's labelling of the pantry: names, folders, sizes, owners of files. Unit 2 · What is an OS?
Fill down Dragging a cell's corner square to copy its formula down a column. Unit 7 · Office and collaborative tools
find Searches a directory tree for files by name, type, size or age — reads the labels on the jars. Unit 4 · Finding information
Fingerprint The short form of a key, for comparing it by eye before you trust a server. Unit 3 · SSH and TLS
Fingerprint (SSH)** A short summary of a server's key, its identity card, compared on the first connection. Unit 6 · SSH remote access
Firewall A filter that decides which traffic a machine accepts. Unit 3 · Configuring TCP/IP on hosts
Firmware Software stored permanently in a chip on the motherboard; the first code the CPU runs at power-on. The card taped to the kitchen wall. Unit 1 · Boot
Flash memory Chips that store bits as electrons trapped in cells, with no power needed. Inside SSDs, USB sticks, phones and SD cards. NAND flash is the kind in SSDs. Unit 1 · Storage
Flatpak A package format for desktop apps that works on any distribution, bundles its dependencies and runs apps in a sandbox. Unit 2 · Package managers
Flooding What a switch does with an unknown destination or a broadcast: sends it out of every other port. Unit 3 · Ethernet, MAC addresses and switching
Focus In diskpart, the disk, partition or volume that the next commands act on, marked with *. Unit 4 · Windows Disk Management
for loop Repeats the same lines once for each item of a list. Unit 4 · Shell scripts
Foreground The command that owns the terminal until it ends; fg brings a job back there. Unit 5 · Processes
Forge A website that hosts Git repositories and adds accounts, permissions and pull requests (GitHub, GitLab, Forgejo) Unit 7 · Git remotes and collaboration
Fork A copy of a project that continues on its own, like OpenTofu from Terraform. Unit 7 · Software by licence and purpose
Form factor A standard size and shape for motherboards (ATX, micro-ATX, mini-ITX) so they fit any matching case. Unit 1 · Motherboard
Formatting Writing a new, empty file system on a partition; a quick format does not erase the old bytes. Unit 4 · File systems
Formula What a cell calculates; it always starts with =. Unit 7 · Office and collaborative tools
Four freedoms Run it, study and change it, copy it, share your changes (numbered 0 to 3) Unit 2 · Software licences
Fragmentation A file stored in several separate pieces of the disk. Unit 4 · File systems
Fragmented (file) A file whose pieces are stored in places that are not next to each other. Unit 5 · Maintenance and optimisation
Frame The link layer's unit: Ethernet header, packet inside, FCS checksum at the end. Unit 3 · How a message travels
Free software Software whose licence gives every user the four freedoms; free as in freedom, not price. Unit 2 · Software licences
Freeware No price, closed recipe (WhatsApp) Unit 2 · Software licences
FSF Free Software Foundation, founded by Stallman in 1985. Unit 2 · Software licences
fstab /etc/fstab, the file that lists which file systems to mount at every boot, where and how. Unit 4 · Mounting file systems
FTP File Transfer Protocol (RFC 959, 1985): moves files but encrypts nothing, not even the password. Unit 7 · File transfer
FTPS The old FTP wrapped in TLS; not the same as SFTP. Unit 7 · File transfer
Full backup A copy of everything, every time. Unit 4 · Backups
Full control The NTFS permission that allows everything, including changing the ACL and taking ownership. Unit 5 · NTFS permissions
Function A named calculation with arguments, like SUM(D2:D11) Unit 7 · Office and collaborative tools
Functional elements The four parts of any computer system: hardware, software, data and users. Unit 2 · What is an OS?

G

Term What it means Where you met it
Gateway (route) The next router a route hands the packet to: the road the sign points to. Unit 3 · Lab 04-01 · The default route
getent Prints entries from the account lists (getent passwd marta, getent group dev) Unit 5 · Users and groups on Linux
Get-Member The cmdlet that asks an object which properties and methods it has. Unit 5 · PowerShell first contact
GHz Gigahertz — one billion cycles per second. It measures how fast the CPU runs its loop, not how "good" the computer is. Unit 1 · Hardware
GID Group identifier: the number of a group. Unit 5 · Users and groups on Linux
Git The most used version control system, written by Linus Torvalds in April 2005; free software (GPL-2) Unit 7 · Git basics
.gitignore A file listing the names and patterns Git must act as if it did not see: secrets, build output, big binaries. Unit 7 · Git basics
Glob A file-name pattern (*, ?, [ ]) that the shell turns into matching names before the command starts. Unit 5 · Back to the shell
Global address A public IPv6 address (starts with 2 or 3), reachable from the Internet unless a firewall blocks it. Unit 3 · IPv6 in 55 minutes
GNU Stallman's project (1983) for a complete free operating system. Unit 2 · Software licences
GPL GNU General Public License, the best-known copyleft licence; the Linux kernel uses version 2. Unit 2 · Software licences
GPT GUID Partition Table: the modern partition table, 128 named partitions and a safety copy at the end of the disk. Unit 4 · Partitions: MBR and GPT
Graphing RouterOS's diary: every 5 minutes it records traffic, CPU, memory and disk, and shows them as graphs. Unit 3 · Lab 09-04 · Graphs
GRE Generic Routing Encapsulation: IP protocol 47, which carries PPTP's data and has no ports at all. Unit 3 · Lab 08-03 · PPTP and SSTP
grep Prints the lines of files that contain a text — opens the jars and looks inside. Unit 4 · Finding information
Group A list of users that gets rights together: one decision for the whole team. Unit 5 · Users and groups on Linux
Group Policy Object (GPO) A named set of settings stored in the domain and linked to a site, the domain or an OU: a rule sheet pinned on a door. Unit 6 · Group Policy and domain resources
Group-Object PowerShell's sort + uniq -c: groups equal values wherever they are, no sorting needed. Unit 5 · Bash and PowerShell side by side
GRUB GRand Unified Bootloader — the usual Linux bootloader, and the menu that lets you choose between Linux and Windows. Unit 1 · Boot
Guest The operating system installed inside a VM. Unit 2 · Virtualisation
GUI Graphical User Interface: windows, icons and a mouse. Unit 2 · OS architecture

H

Term What it means Where you met it
Handshake The moment the two ends of a WireGuard tunnel prove their keys to each other; no handshake, no tunnel. Unit 3 · VPN with WireGuard
Hardening Making a system harder to break: remove what it does not need, close what is open by default. Unit 6 · Why protect systems
Hardware offloading The switch chip forwards frames between its own ports, so the CPU never sees them (flag H). Unit 3 · Lab 03-02 · Bridge performance
Hash A fixed-size fingerprint of a password: it can be checked against, never turned back. Unit 5 · Users and groups on Linux
Hash (ECMP) A quick fingerprint number from a packet's addresses that keeps one conversation on one ECMP path. Unit 3 · Lab 04-04 · ECMP
Hash function The calculation that reads a whole file and gives back its fixed-size checksum. Unit 2 · Verify an ISO
HDD Hard Disk Drive — a disk that stores bits on spinning magnetic platters. Slow and cheap: the classic pantry. Unit 1 · Hardware
HDMI High-Definition Multimedia Interface — the TV/console connector carrying digital video and audio in one cable. Unit 1 · Peripherals
HEAD Git's name for the commit you are standing on: the last photo. Unit 7 · Git basics
Header The control information a layer writes on its envelope: addresses, numbers, flags. Unit 3 · How a message travels
Headers The lines at the top of an email (From, To, Subject, Received) Unit 7 · Email and messaging
Hexadecimal Base 16, digits 0–9 then A–F. A shorthand for bits: one hex digit = exactly 4 bits, so a byte is always 2 hex digits (0100 1000 → 48). Unit 1 · Binary
Hidden file A file whose name starts with a dot; ls skips it, ls -a and find show it. Unit 4 · Terminal survival and the directory tree
Hide SSID Stops an AP announcing its name in beacons; not security, since every client still says the name out loud. Unit 3 · Lab 05-03 · Your own access point
High availability A cluster feature that restarts a VM on another node when its node dies. Unit 2 · Proxmox VE
Home directory Your own folder, /home/<name>, written ~. Unit 4 · Terminal survival and the directory tree
Hop One router a packet passes through on its way. Unit 3 · Routing
Hop-by-hop routing Every router chooses only the next hop, from its own table; nobody plans the whole path. Unit 3 · Lab 04-03 · Static routing through a neighbour
Host The real machine, with its own OS, that runs the VMs. Unit 2 · Virtualisation
Host firewall A firewall running on one machine that protects only that machine (e.g. ufw) Unit 3 · Ports and firewalls
Host key An SSH server's own key; your client remembers it in ~/.ssh/known_hosts and checks it every time. Unit 3 · SSH and TLS
Hostname The name a machine gives itself, stored in /etc/hostname. Unit 5 · Configuring the system by command
HTTPS HTTP inside TLS, on TCP port 443: the web in a sealed envelope. Unit 3 · SSH and TLS
Hub The switch's ancestor: it repeated every frame to everybody. Unit 3 · Ethernet, MAC addresses and switching
Huffman coding A compression method that gives short codes to frequent symbols and long codes to rare ones (like Morse: E = one dot). Unit 1 · Data
Hybrid kernel A small core plus services kept inside for speed (Windows, macOS) Unit 2 · OS architecture
Hypervisor The coordinator that creates VMs and shares the real hardware among them. Unit 2 · Virtualisation

I

Term What it means Where you met it
IANA The world's central stock of IP addresses; it ran out of IPv4 on 3 February 2011. Unit 3 · NAT and Internet access
icacls The Windows command that shows and changes NTFS ACLs (/grant, /deny, /inheritance:r) Unit 5 · NTFS permissions
ICMP The internet layer's helper protocol that ping uses; it rides directly inside IP, with no port. Unit 3 · How a message travels
ICMP echo request / reply The question and answer of ping; the time between them is the RTT. Unit 3 · Lab 09-02 · Ping and Netwatch
ICMP redirect A router's message "there is a shorter way: next time send it straight to that router". Unit 3 · Lab 04-03 · Static routing through a neighbour
IDE Integrated Development Environment: editor, build button and debugger in one program, the developer's workbench. Unit 5 · What a development machine needs
Identity A RouterOS router's name, shown in the prompt. Unit 3 · Meet RouterOS
IEEE 802.11 The standard behind Wi-Fi (first version 1997) Unit 3 · Wireless LAN
Image (container)** The packed, read-only template a container starts from: the recipe, not the dish. Unit 6 · Containers
IMAP Internet Message Access Protocol: the rules to look into your box, which stays on the server. Unit 7 · Email and messaging
Import-Csv Reads a CSV and turns each line into an object whose properties are named after the header. Unit 5 · Bash and PowerShell side by side
Incremental backup A copy of what changed since the last backup of any kind: "what happened today" in the diary. Unit 4 · Backups
Information Data with meaning — or, in Shannon's words, "the reduction of uncertainty". Unit 1 · Data
Inheritance New files and subfolders copy their parent folder's ACL entries, marked (I) in icacls. Unit 5 · NTFS permissions
Initialize In Windows, writing an empty partition table (GPT or MBR) on a new disk. Unit 4 · Windows Disk Management
Inode The card a file system keeps for each file: size, owner, dates, which blocks — everything except the name. Unit 4 · File systems
Installation plan The written answers to seven questions before installing: what, where, from what, disk, existing data, who, after. Unit 2 · Planning an installation
Installer The program that puts an operating system on an empty disk — an interview: it asks, copies, and makes the disk bootable. Unit 2 · Installing Debian
Integrity Nobody changed the data without permission. Unit 6 · Why protect systems
Interface The agreed way a peripheral connects: plug shape, wires and rules for talking (USB, HDMI, Bluetooth...). Unit 1 · Peripherals
I/O Input/Output — the doors to the outside world: keyboard, mouse, screen, network card, sensors... Some doors swing both ways. Unit 1 · Hardware
Interface queue The queue every packet goes through as it leaves a port; one place to attach a queue type. Unit 3 · Lab 07-05 · PCQ
IP pool A named range of addresses that RouterOS services (DHCP, PPP) hand out automatically. Unit 3 · Lab 08-02 · PPPoE server
iperf3 The speed-measuring tool: a client sends as much as it can to a server and reports bits per second. Unit 3 · Lab 07-01 · Simple queue
IPP Internet Printing Protocol, TCP 631, spoken by CUPS and by modern printers. Unit 6 · Print server
IPv4 address A 32-bit number in four octets (dotted decimal): your street and house number. Unit 3 · IPv4 addressing
IPv6 The successor of IPv4: 128-bit addresses written as 8 groups of 4 hex digits, 2⁹⁶ times more addresses than IPv4. Unit 3 · IPv6 in 55 minutes
IRC Internet Relay Chat (Jarkko Oikarinen, 1988), the oldest ancestor of team messaging. Unit 7 · Email and messaging
ISA Instruction Set Architecture — the "language" a CPU understands. x86-64 and ARM are the two big families. Unit 1 · CPU
ISO image One file holding an exact copy of an installation disc. Unit 2 · Your first VM

J

Term What it means Where you met it
Jail In fail2ban, the rules for one service: which log, how many failures, how long the ban. Unit 6 · Basic security utilities
JAVA_HOME Environment variable many tools read to find the JDK; empty until you set it. Unit 5 · What a development machine needs
JDK Java Development Kit: compiler, runtime and tools to make Java programs (the JRE only runs them) Unit 5 · What a development machine needs
Job A command started from one shell, numbered %1, %2... inside that shell only. Unit 5 · Processes
Job (print)** A document sent to print, waiting with its ticket in the queue. Unit 6 · Print server
Joining Registering a computer in a domain so that it accepts the domain's users. Unit 6 · Joining a domain
Journal A notebook where the file system writes what it is about to do, so it can recover after a power cut. Unit 4 · File systems
journalctl The command that asks the journal questions: by unit, boot, time, priority. Unit 5 · Logs and journald
JVM Java Virtual Machine: the runtime that runs Java bytecode on any real computer. Unit 5 · What a development machine needs

K

Term What it means Where you met it
KB number The code Microsoft gives each Windows update. Unit 2 · Software and updates on Windows
KDC Key Distribution Centre: the service on the DC that checks your password once and hands out tickets (the festival entrance). Unit 6 · Domains and directory services
Kerberos The protocol that proves who you are with tickets, so your password never reaches the services: the festival wristband. Unit 6 · Domains and directory services
Kernel The core of the operating system: controls the hardware and shares it among all other programs. The head chef once the kitchen is open. Unit 1 · Boot
Kernel mode The CPU's back room: every instruction allowed, all hardware reachable; only the kernel works there. Unit 2 · OS architecture
Kernel panic Linux's version of the blue screen: the kernel stops on purpose after a fatal error in kernel mode. Unit 2 · OS architecture
Key pair A private key that never leaves the machine and a public key you give to the other side. Unit 3 · VPN with WireGuard
Knowledge What you get when you connect information with what you already know and use it to make decisions. Data → information → knowledge. Unit 1 · Data
KRACK Mathy Vanhoef's 2017 attack on the WPA2 handshake, fixed by updates. Unit 3 · Wireless LAN
KVM Kernel-based Virtual Machine: the Linux kernel module that runs guests on the real CPU. Unit 2 · Virtualisation

L

Term What it means Where you met it
Lab report The course's write-up of a practical, so someone else could repeat it. Unit 2 · Markdown lab reports
Label A short name given to a file system with mkfs -L (LABEL), different from the partition's name (PARTLABEL) Unit 4 · File systems
Ladder (troubleshooting) The six-rung bottom-up method: link, address, gateway, path, names, service; climb in order and stop at the first rung that fails. Unit 3 · Network troubleshooting
LAN Local Area Network — the network inside one place: your home, your school. Coming up in Unit 1 · Networking. Unit 1 · Networking
Lane One send + receive pair of connections in PCIe. Devices use 1, 4 or 16 side by side (x1, x4, x16). Unit 1 · Motherboard
Layer A group of protocols that solves one problem of the trip and trusts the layer below for the rest. Unit 3 · How a message travels
LDAP Lightweight Directory Access Protocol (port 389): the language for asking the directory questions. Unit 6 · Domains and directory services
Lease The time an address is lent for; renewed at half. Unit 3 · DHCP and DNS
Lease script A small RouterOS script that runs when a lease is granted, renewed or released. Unit 3 · Lab 02-02 · Static DHCP leases
Least privilege Give each person only the rights their job needs — like a read-only account that can look and never touch. Unit 2 · Proxmox VE
libvirt The service that keeps the list of VMs and starts and stops them. Unit 2 · Virtualisation
Licence The author's written permission: what others may do with the software, and on what conditions. Unit 2 · Software licences
limit-at (CIR) A queue's guaranteed rate: the client's reserved lane, which nobody else may take. Unit 3 · Lab 07-03 · Guaranteed bandwidth
Link-local address 169.254.x.x: what a machine gives itself when nobody gave it an address. Unit 3 · IPv4 addressing
Live migration Moving a running VM to another node without switching it off. Unit 2 · Proxmox VE
Live system A complete OS that starts from the disc and runs in RAM without installing; forgets everything at restart. Unit 2 · Your first VM
Load average Average number of processes running or waiting for a CPU (and, on Linux, the disk) over 1, 5 and 15 minutes; compare it with the cores. Unit 5 · Monitoring performance
Local account A user that exists only on one computer, like student on the lab VMs. Unit 2 · Installing Windows 11
Local resource Something useful that is inside or plugged into your own machine. Unit 6 · Clients, servers and shared resources
Local Security Policy The Windows console (secpol.msc) where one PC's rights and security options live. Unit 6 · User rights and security policies
Locale The rules a system uses for the language of messages, dates and decimal points, e.g. en_US.UTF-8. Unit 2 · Installing Debian
Localhost 127.0.0.1, the address a machine uses to talk to itself. Unit 3 · Ports and firewalls
Locally administered address A MAC made up by software (second hex digit 2, 6, a or e): VMs, containers, phones. Unit 3 · Ethernet, MAC addresses and switching
locate Finds files by name instantly from a list made in advance; can miss files newer than the list. Unit 4 · Finding information
Locked account An account whose password can no longer match (passwd -l); it and its files still exist. Unit 5 · Users and groups on Linux
Lockout Blocking an account for a while after several failed logins. Unit 5 · Account and password policies
Log A diary of short timestamped lines the system writes while things happen. Unit 5 · Logs and journald
Log prefix A short text a firewall rule stamps on its log lines, so you can find them later. Unit 3 · Lab 06-04 · Firewall logging
Log topic A label on every RouterOS log message (system, dhcp, error...) that decides where it is written. Unit 3 · Lab 09-07 · Logs, supout.rif and documenting the router
Logical partition A partition inside an MBR extended partition; Linux numbers them from 5. Unit 4 · Partitions: MBR and GPT
Logical volume (LV) A section cut from a volume group; the piece you format and mount. Unit 4 · LVM and RAID
Logon right A Windows user right that decides who may sign in, and how (keyboard, network, Remote Desktop). Unit 6 · User rights and security policies
Longest prefix match When several routes match, the most specific one (longest prefix) wins: "Hospital" beats "City centre". Unit 3 · Lab 04-01 · The default route
Loopback 127.0.0.0/8: the machine talking to itself. Unit 3 · IPv4 addressing
Loopback bridge A bridge with no ports: it is never unplugged, so an address on it is always up. Unit 3 · Lab 03-02 · Bridge performance
Lossless Compression that rebuilds the exact original file (ZIP, PNG). Nothing is thrown away. Unit 1 · Data
Lossy Compression that permanently drops detail you (hopefully) won't miss (JPEG, video streaming). Smaller files, but no way back. Unit 1 · Data
LOWER_UP The ip link flag that means layer 1 is alive: a working cable and something at the other end. Unit 3 · Cabling a LAN
LSDOU The order GPOs are applied in: local, site, domain, OU; the last one wins. Unit 6 · Group Policy and domain resources
LTS Long-term support: a release that gets security updates for years (five for Ubuntu LTS). Servers use them. Unit 2 · Ubuntu Server and first steps
LVM A layer that lets the installer hand out disk space flexibly, keeping some in reserve to grow the system later without reinstalling. Unit 2 · Ubuntu Server and first steps
LXC The container technology Proxmox VE uses; containers are made from templates. Unit 2 · Proxmox VE
lynis An audit tool that inspects a system and gives suggestions and a hardening index; it fixes nothing. Unit 6 · Basic security utilities

M

Term What it means Where you met it
M.2 Small slot and stick shape for SSDs on the motherboard. Only a shape: an M.2 stick can be NVMe (fast) or SATA (slow). Unit 1 · Storage
MAC address Media Access Control address — the unique hardware ID of a network card: 6 bytes written in hex, e.g. A4:5E:60:D2:1B:03. Unit 1 · Binary
MAC address table The switch's list of which MAC lives behind which port (also called fdb) Unit 3 · Ethernet, MAC addresses and switching
MAC spoofing Copying an allowed MAC address onto your own device; why MAC-based lists are not real security. Unit 3 · Lab 05-05 · Snooper, registration table and access list
MAC-Telnet / MAC WinBox A terminal or WinBox session sent in plain Ethernet frames to a MAC address: no IP needed, same room only. Unit 3 · Lab 01-01 · Getting in
Mail client The program where you write and read mail (Thunderbird, Gmail web) Unit 7 · Email and messaging
Mail server The always-on post office that sends, receives and keeps your mail. Unit 7 · Email and messaging
Maintenance The regular tidy-up that keeps a system working well: nothing new is cooked, but tomorrow's service is faster. Unit 5 · Maintenance and optimisation
MAN Metropolitan Area Network — a network covering a city. Unit 1 · Networks
Man page The full manual of a command, installed with it; opened with man, searched with /word. Unit 7 · Finding technical documentation
Man-in-the-middle An attacker between you and the server who pretends to be the server. Unit 3 · SSH and TLS
Manual section The number in brackets after a man page name: 1 commands, 5 file formats, 8 administration. Unit 7 · Finding technical documentation
Markdown Plain text with a few marks (#, *, -) that a preview turns into headings, lists and code; files end in .md. Unit 2 · Markdown lab reports
Mask The ceiling of an ACL: no extra line can give more than it; getfacl shows the result as #effective:. Unit 5 · Special permissions and ACL
Masquerade Source NAT: outgoing packets leave with the router's own public address. Unit 3 · NAT and Internet access
max-limit (MIR) The most a queue lets a client have: the toll gate's top speed. Unit 3 · Lab 07-01 · Simple queue
Mbps vs MB/s The ÷8 trap: connection speed is measured in megabits per second, file sizes in megabytes. 8 bits = 1 byte, so 300 Mbps ≈ 37.5 MB/s. Unit 1 · Data
MBR Master Boot Record: the 1983 partition table, 4 primary partitions and at most 2 TiB. Unit 4 · Partitions: MBR and GPT
mdadm The Linux tool to build and manage software RAID. Unit 4 · LVM and RAID
Memory hierarchy Registers → cache → RAM → storage: the closer to the CPU, the faster, smaller and more expensive per byte. Unit 1 · Memory
Mention @name, to call one person into the conversation. Unit 7 · Email and messaging
Merge Joining a branch's commits into another branch. Unit 7 · Git remotes and collaboration
Merge conflict Two commits changed the same lines, so Git stops and asks a human to choose. Unit 7 · Git remotes and collaboration
Method An action an object knows how to do, called with a dot: (Get-Date).AddDays(100). Unit 5 · PowerShell first contact
MIB The files that give OIDs readable names; without them an SNMP tool shows only numbers. Unit 3 · Lab 09-05 · SNMP
Microkernel A tiny back room: only the essentials in kernel mode, drivers as normal processes (MINIX) Unit 2 · OS architecture
Microprocessor A whole CPU on a single chip. The first commercial one was the Intel 4004 (1971). Unit 1 · CPU
Microsoft account An online account with an e-mail address, which Windows 11 pushes during setup. Unit 2 · Installing Windows 11
Microsoft Store Windows' app store: Microsoft checks the apps and updates them automatically. Unit 2 · Software and updates on Windows
MIMO Multiple input, multiple output: several antennas sending in parallel for more speed. Unit 3 · Lab 05-01 · Wireless basics and your radio name
Minimum requirements The least hardware with which a system starts, not runs well. Unit 2 · Planning an installation
Mirror One of many servers around the world holding identical copies of a distribution's packages. Unit 2 · Installing Debian
mkfs Make file system: the command family (mkfs.ext4, mkfs.xfs...) that formats a partition. Unit 4 · File systems
MNDP MikroTik Neighbor Discovery Protocol: routers shout "here I am" every 30 seconds so WinBox can list them. Unit 3 · Lab 01-01 · Getting in
Modify The NTFS permission to read, write, run and delete; the one you give employees, never Full control. Unit 5 · NTFS permissions
Module A piece of the Linux kernel (usually a driver) loaded only when its device is present. Unit 2 · OS architecture
Monolithic kernel One big back room: scheduler, memory, file systems and drivers all in kernel mode (Linux) Unit 2 · OS architecture
Motherboard The building: the main circuit board that holds every component and carries the buses that connect them. Unit 1 · Motherboard
Mount point The ordinary, empty directory where a file system is attached: the door to the room. Unit 4 · Mounting file systems
Mounting Attaching a file system to a directory of the Linux tree so you can reach it; nothing is copied. Unit 4 · Mounting file systems
MPPE Microsoft Point-to-Point Encryption, PPTP's RC4-based encryption; it only works with MS-CHAP. Unit 3 · Lab 08-03 · PPTP and SSTP
MS-CHAPv2 The PPP login method to pick over PAP; in 2012 a captured MS-CHAPv2 login was shown to be crackable. Unit 3 · Lab 08-02 · PPPoE server
MTU The biggest packet that fits in one frame: 1500 bytes on Ethernet. Unit 3 · Ethernet, MAC addresses and switching
Multicast An address for a group of machines; ff02::1 means everybody on this cable. Unit 3 · IPv6 in 55 minutes
MX record The DNS record that says which machine receives a domain's mail. Unit 7 · Email and messaging

N

Term What it means Where you met it
Named volume Storage that Podman creates and manages outside any container, right for databases. Unit 6 · Images, volumes and ports
nano A simple text editor that runs inside the terminal. Unit 4 · Mounting file systems
NAT Network Address Translation: the host swaps the guest's private address for its own; the guest can go out, nobody can come in. Unit 2 · Your first VM
NAT helper A RouterOS fix for protocols (FTP, SIP, PPTP) that write IP addresses inside their messages, where plain NAT does not look. Unit 3 · Lab 06-07 · Source NAT and masquerade
Neighbour Discovery IPv6's replacement for ARP: multicast messages to find a neighbour's MAC address (ip -6 neigh) Unit 3 · IPv6 in 55 minutes
Nested virtualisation Running a hypervisor inside a virtual machine: a VM in a VM, like Russian dolls. Unit 2 · Proxmox VE
NetBIOS name The short old-style name of a domain, up to 15 characters: TRAMUNTANA. Unit 6 · Domains and directory services
Netinst A small installation image that downloads the rest during the install. Unit 2 · Planning an installation
Netinstall MikroTik's program that reinstalls RouterOS on a router booted from the network, formatting its storage. Unit 3 · Lab 01-07 · Reinstall RouterOS with Netinstall
Netplan Ubuntu's network configuration tool, written in YAML files in /etc/netplan/. Unit 6 · Clients, servers and shared resources
Netwatch Probes a host again and again and runs an up-script or down-script when it changes state. Unit 3 · Lab 09-02 · Ping and Netwatch
Network Two or more devices connected to exchange information: devices + medium + protocols. Unit 1 · Networks
Network address Host bits all 0: the name of the street, never given to a machine. Unit 3 · IPv4 addressing
Network part / host part The street (same for all neighbours) and the house number (yours) inside an IP address. Unit 3 · IPv4 addressing
Network resource Something useful another machine gives you through the network: a share, a printer, a web app. Unit 6 · Clients, servers and shared resources
NetworkManager The service that manages the network on Debian's desktop; its command is nmcli. Unit 3 · Configuring TCP/IP on hosts
NFS Network File System (Sun, 1984, TCP 2049): the staff door that trusts machines and UID numbers. Unit 6 · NFS
NIC Network Interface Card — the part of a device that connects it to a network; the door of the house. Unit 1 · Networks
Nice value A process's place in the queue for the chef, from −20 (first) to 19 (last); default 0. Unit 5 · Processes
NIST The US National Institute of Standards and Technology; its SP 800-63B sets today's password advice. Unit 5 · Account and password policies
Node One physical server in a Proxmox datacentre. Unit 2 · Proxmox VE
nofail An /etc/fstab option: if this disk is missing, keep booting. Unit 4 · Mounting file systems
Non-volatile Memory that keeps its contents without power — the disk. Unit 1 · Hardware
Note (RouterOS) A message every administrator sees when they log in to the router. Unit 3 · Lab 01-03 · Packages, release channels and upgrades
NTFS The Windows file system (1993), with a journal and per-user permissions; Windows' system disk must use it. Unit 4 · File systems
NTP Network Time Protocol: keeps the clock right by asking time servers on the Internet. Unit 5 · Configuring the system by command
NVMe Non-Volatile Memory Express (2011) — protocol for SSDs over PCI Express: thousands of MB/s instead of SATA's ~550. Unit 1 · Storage
NXDOMAIN DNS's correct answer "this name does not exist". Unit 3 · DHCP and DNS

O

Term What it means Where you met it
OAuth You sign in at the provider's own page, and the program gets a limited key instead of your password. Unit 7 · Email and messaging
Object What the PowerShell pipe carries: a form with labelled fields instead of a sheet of text. Unit 5 · PowerShell first contact
OCI Open Container Initiative (2015): the open standard that lets any tool run any image. Unit 6 · Containers
Octal notation Permissions as three digits with r=4, w=2, x=1: 640 = rw-r-----. Unit 5 · Linux permissions
Octet One of the four 8-bit pieces of an IPv4 address, from 0 to 255. Unit 3 · IPv4 addressing
ODF Open Document Format (.odt, .ods, .odp), LibreOffice's native format: a ZIP box of XML files. Unit 7 · Office and collaborative tools
OEM licence Installed by the computer's maker and tied to that one device. Unit 2 · Software licences
Office suite The set of general-purpose office programs: word processor, spreadsheet and presentations. Unit 7 · Office and collaborative tools
Off-site Kept in another place, so a fire or a thief cannot take it with the original. Unit 4 · RAID is not a backup
OID Object Identifier: the numbered shelf of one value in the SNMP tree, like 1.3.6.1.2.1.1.5.0 for the device name. Unit 3 · Lab 09-05 · SNMP
ONT Optical Network Terminal — the box where home fibre ends; turns light into electrical signals and back. Unit 1 · Networks
OOXML Office Open XML (.docx, .xlsx, .pptx), Microsoft Office's native format: also a ZIP box of XML. Unit 7 · Office and collaborative tools
Open source The 1998 name for (almost) the same licences, stressing a better way to build software. Unit 2 · Software licences
OpenSSH The free SSH program almost everyone uses (since 1999) Unit 3 · SSH and TLS
Optimisation Arranging the system so it does less work for the same result. Unit 5 · Maintenance and optimisation
Option The part of a command line that changes how it works, starting with -: the -l in ls -l. Unit 4 · Terminal survival and the directory tree
Organisational unit (OU) A folder in the directory tree where an object is filed and rules are attached: the room where your desk is. Unit 6 · Domain users, groups and OUs
Orphan A dependency that nothing needs any more; apt autoremove takes it out. Unit 2 · Package managers
OS Operating System — the program that manages the hardware and lets all other programs run (Windows, Linux, Android...). Unit 2 · Operating systems
OSI (Open Source Initiative)** The organisation founded in 1998 to promote open source. Careful: not the OSI network model. Unit 2 · Software licences
OSI model A 7-layer map that splits how networks work into small, stackable steps — from physical wires to applications. Unit 1 · Networking
Others Everybody who is neither the owner nor in the file's group; the third triplet. Unit 5 · Linux permissions
OUI The first 3 bytes of a MAC address: the manufacturer's code, sold by the IEEE. Unit 3 · Ethernet, MAC addresses and switching
Owner The one user a file belongs to; the first triplet of its card. Unit 5 · Linux permissions

P

Term What it means Where you met it
Package One file with a program plus a label: its name, version and what it needs. .deb on Debian and Ubuntu. Unit 2 · Package managers
Package (RouterOS) An .npk file that adds a group of features, compiled for one CPU architecture only. Unit 3 · Lab 01-03 · Packages, release channels and upgrades
Package manager The program that downloads, checks, installs and removes packages from a repository — apt, winget... Unit 2 · Package managers
Packet The internet layer's unit: an IP header plus what it carries. Unit 3 · How a message travels
Packet analyser (sniffer) A program that copies and decodes every frame reaching your card, like a photocopier at your letterbox. Unit 3 · Wireshark: first capture
PAM Pluggable Authentication Modules: the chain every Linux login passes through, configured in /etc/pam.d/. Unit 5 · Account and password policies
pam_faillock The PAM module that locks an account after too many wrong passwords. Unit 5 · Account and password policies
pam_pwquality The PAM module that refuses short or obvious passwords (minlen, dictionary check) Unit 5 · Account and password policies
PAN Personal Area Network — a network of a few metres around one person, like Bluetooth headphones. Unit 1 · Networking
Pandoc A converter between document formats (Markdown to HTML, Word, Typst...) that changes notation, not content. Unit 7 · Docs as code
PAP A PPP login method that sends the password as plain text: avoid it. Unit 3 · Lab 08-02 · PPPoE server
Parent directory The directory one level up, written ... Unit 4 · Terminal survival and the directory tree
Parent queue A queue whose max-limit is the whole road, shared among its child queues. Unit 3 · Lab 07-03 · Guaranteed bandwidth
Parity A check value (bit-by-bit sum without carry) that lets RAID 5 and 6 rebuild a dead disk. Unit 4 · LVM and RAID
Partition A piece of a disk that the system treats as a separate disk: a labelled shelf in the pantry. Unit 2 · Planning an installation
Partition table The small map at the start of a disk that says where each partition starts and ends (MBR or GPT) Unit 4 · Partitions: MBR and GPT
Passphrase A password (usually long) used as the key to encrypt and decrypt. Unit 4 · Compression, encryption, integrity
Password policy The rules the system enforces on passwords: length, quality, ageing. Unit 5 · Account and password policies
Patch Tuesday The second Tuesday of each month, when Microsoft publishes its security updates. Unit 2 · Software and updates on Windows
Path The address of a file or directory in the tree, such as /home/marta/notes.txt. Unit 4 · Terminal survival and the directory tree
pcap A file that stores captured frames to open later. Unit 3 · Wireshark: first capture
PCIe PCI Express — the main high-speed bus in a PC, built from lanes. Each generation roughly doubles the speed per lane. Unit 1 · Motherboard
PCQ Per Connection Queuing: one rule that gives every client (sub-stream) its own queue with the same rate. Unit 3 · Lab 07-05 · PCQ
Peer In WireGuard, the other side of the tunnel, known by its public key. Unit 3 · VPN with WireGuard
Peripheral Any device connected from outside to bring information in, send it out, do both, or store it. Unit 1 · Peripherals
Permission The OS's rule about which user may touch which file or device. Unit 2 · What is an OS?
Permissive licence Almost no conditions: keep the author's name; closed products allowed (MIT, BSD, Apache) Unit 2 · Software licences
Phishing A fake message pretending to come from someone you trust, to make you click, log in or pay. Unit 7 · Email and messaging
Physical volume (PV) A disk or partition handed to LVM: one pack of blank sheets for the binder. Unit 4 · LVM and RAID
PID Process ID: the number the OS gives every running process. Unit 2 · What is an OS?
Ping Sends an ICMP echo request and waits for the reply: is it alive, and how far away is it? Unit 3 · Lab 09-02 · Ping and Netwatch
Pipe The vertical bar character: sends what one command prints into the next command as its input. Unit 4 · Finding information
Pipeline A chain of small commands joined by pipes, each doing one small job. Unit 5 · Back to the shell
Plain text A file of characters only, with no hidden formatting; opens anywhere. Unit 2 · Markdown lab reports
Plug and play The computer detects, identifies and configures a new device automatically, using the IDs the device announces. Unit 1 · Peripherals
Podman A container tool with Docker's commands but no daemon and no need for root. Unit 6 · Containers
Point release The normal fixes for a version, collected, such as Debian 13.0 → 13.7. Same system, newer corrections. Unit 2 · Installing Debian
Point-to-point address A tunnel address whose "network" is the other end of the tunnel, which is also your gateway. Unit 3 · Lab 08-01 · PPPoE client
POP3 The older protocol that downloads mail to one device. Unit 7 · Email and messaging
Port The number that picks the right program inside a computer (443 = HTTPS): the name on the inner envelope. Unit 3 · How a message travels
Port forwarding A standing order (dst-nat) sending one WAN port to one machine inside the LAN. Unit 3 · NAT and Internet access
Port publishing -p host:container: a corridor from a port of the server to a port inside the box. Unit 6 · Containers
Port scanner A program that knocks on every port of a machine and reports which answer (nmap). Unit 6 · Basic security utilities
POST Power-On Self-Test — the firmware's quick check of CPU, RAM and graphics. When it fails, the PC beeps or blinks an LED. Unit 1 · Boot
PowerShell Windows' modern shell (2006, Jeffrey Snover) whose pipes carry objects instead of text. Unit 5 · PowerShell first contact
PPID Parent Process ID: the PID of the process that started this one. Unit 5 · Processes
PPP Point-to-Point Protocol (RFC 1661, 1994): links exactly two devices and handles login, address and packing. Unit 3 · Lab 08-01 · PPPoE client
PPP profile Settings applied to every PPP client that uses it: server address, client pool, DNS, encryption. Unit 3 · Lab 08-02 · PPPoE server
PPP secret One user in the router's PPP user database: name, password, profile. Unit 3 · Lab 08-02 · PPPoE server
pppd The Linux PPP daemon; with its pppoe plugin it is a PPPoE client. Unit 3 · Lab 08-02 · PPPoE server
PPPoE A way for a router to get its WAN connection by logging in with a user name and password. Unit 3 · NAT and Internet access
PPPoE discovery The broadcast "is there any PPPoE server here?" (PADI, PADO, PADR, PADS) that needs no IP address. Unit 3 · Lab 08-01 · PPPoE client
PPTP Point-to-Point Tunneling Protocol (1999): PPP over IP with tcp/1723 and GRE; broken, avoid it. Unit 3 · Lab 08-03 · PPTP and SSTP
Prefix The number of ones in the mask, written /24. Unit 3 · IPv4 addressing
Prefix rule In a decodable code, no codeword may be the beginning of another one. That is how a receiver splits the bit stream without separators. Unit 1 · Data
Primary group The one group each user has (field 4 of /etc/passwd); new files get it. Unit 5 · Users and groups on Linux
Primary partition One of the four main entries of an MBR partition table. Unit 4 · Partitions: MBR and GPT
Principle of least privilege Give each account only the keys its job needs: the back-door key, not the master key. Unit 5 · sudo and least privilege
Print server A service that receives jobs from the clients, keeps them in a queue and feeds the printer. Unit 6 · Print server
Priority (severity) How bad a log line is, from 0 (emerg, worst) to 7 (debug) Unit 5 · Logs and journald
Private address An address from the RFC 1918 blocks (10/8, 172.16/12, 192.168/16), never routed on the Internet. Unit 3 · IPv4 addressing
Private key The secret half of a key pair (id_ed25519): it proves who you are and never travels. Unit 6 · SSH remote access
Private MAC address A made-up MAC a phone uses per network so it cannot be tracked. Unit 3 · Wireless LAN
Privilege A Windows user right to do a system action, such as SeShutdownPrivilege. Unit 6 · User rights and security policies
PRL Prevención de riesgos laborales — occupational risk prevention; in Spain, Ley 31/1995. Unit 1 · Health and safety
Process A program that is running; one sheet on the chef's desk. Unit 2 · What is an OS?
Program A list of instructions written by a human and stored in the machine. No magic: the computer blindly follows it, step by step. Unit 1 · Hardware
Prompt The text the shell prints while it waits for a command, e.g. student@ubu-srv:~$ — who, where, which folder. Unit 2 · Ubuntu Server and first steps
Property One labelled field of an object, asked for by name (WorkingSet64, Status) Unit 5 · PowerShell first contact
Proprietary software Software that keeps its recipe secret and gives you a limited permission. Unit 2 · Software licences
Protocol The agreed rules two devices follow to talk — without a common one, no communication. Unit 1 · Networks
Provisioning Creating a domain: the directory database, the DNS zone, the Kerberos keys and the first administrator. Unit 6 · Domains and directory services
Proxmox VE A free type 1 hypervisor built on Debian, managed from a browser on port 8006. Unit 2 · Proxmox VE
Proxy A middleman that answers or fetches on your behalf. Unit 3 · Lab 06-06 · Redirect
PSK Pre-shared key: one Wi-Fi password shared by every client (WPA2/WPA3 Personal). Unit 3 · Lab 05-03 · Your own access point
Public address An IP address unique in the world, reachable across the Internet. Unit 3 · NAT and Internet access
Public key The half of a key pair made to be given away; it goes into authorized_keys on the server. Unit 6 · SSH remote access
Pull request A page on the forge proposing to merge a branch into main, where others review and comment first (GitLab: merge request) Unit 7 · Git remotes and collaboration
PVID Port VLAN ID: the sticker a switch puts on untagged frames coming in on that port. Unit 3 · VLANs

Q

Term What it means Where you met it
qcow2 QEMU's disk-file format; it grows only as the guest writes. Unit 2 · Your first VM
QEMU The program that imitates a VM's devices: disk, network card, screen. Unit 2 · Virtualisation
QoS Quality of service: how well a network serves its users, how fast, how stable, how fair. Unit 3 · Lab 07-01 · Simple queue
Queue (print)** The line where print jobs wait in order, like bakery tickets. Unit 6 · Print server
Queue (network) A toll gate for packets: it lets them through at a set pace and makes the rest wait or drops them. Unit 3 · Lab 07-01 · Simple queue
Queue type A queuing recipe (like a PCQ) that does nothing until you attach it to a queue. Unit 3 · Lab 07-05 · PCQ

R

Term What it means Where you met it
Radio name A label a RouterOS station sends to a RouterOS AP, shown in its registration table. Unit 3 · Lab 05-01 · Wireless basics and your radio name
RAEE Residuos de aparatos eléctricos y electrónicos — e-waste. Goes to a punto limpio, never the bin (RD 110/2015). Unit 1 · Health and safety
RAID Redundant Array of Independent Disks: several disks combined into one volume that can survive a dead disk. Unit 4 · LVM and RAID
RAM Random Access Memory — the workspace. Fast, small, volatile. "Random access" = jump to any position instantly, like picking any song from a playlist. Unit 1 · Hardware
Range A block of cells from the first to the last, like D2:D11. Unit 7 · Office and collaborative tools
Ransomware A program that locks your files and asks for money to unlock them, like WannaCry in 2017. Unit 2 · Software and updates on Windows
Rate limiting Not letting some traffic go faster than a chosen speed; also called shaping. Unit 3 · Lab 07-01 · Simple queue
Raw (firewall) A firewall table that sees packets before connection tracking, so its rules can mark traffic to skip tracking. Unit 3 · Lab 06-08 · Connection tracking
RDP Remote Desktop Protocol (Microsoft, 1998, port 3389): gives you a session on a far machine. Unit 6 · Remote desktop
Realm In Proxmox's login, the place where your user is defined (Linux PAM or Proxmox VE's own). Unit 2 · Proxmox VE
realmd The Linux tool (realm command) that discovers and joins a domain. Unit 6 · Joining a domain
Recommended requirements The hardware you need to work comfortably; what a plan uses. Unit 2 · Planning an installation
Recovery mode A GRUB menu entry that starts Debian with almost nothing and gives a root shell to repair it. Unit 2 · Snapshots and recovery
Recursive route A route whose gateway is not directly connected, so the router looks it up in the table again. Unit 3 · Lab 04-05 · Recursive routing and failover
Redirect (NAT) A dst-nat that sends a packet to the router itself, optionally on another port: everyone goes to reception. Unit 3 · Lab 06-06 · Redirect
Redirection Telling the shell where a stream goes: > empties and writes, >> appends, 2> errors, < reads from a file. Unit 5 · Back to the shell
Redundancy Extra information stored so that data survives when a disk dies. Unit 4 · LVM and RAID
Reference A citation complete enough for a stranger to find the source again: title, publisher, address, date read. Unit 7 · Finding technical documentation
Register A tiny, ultra-fast storage slot inside the CPU, holding the values being used right this moment. Unit 1 · Hardware
Registration table The access point's list of connected clients and their signal. Unit 3 · Wireless LAN
Registry A server that stores container images, like an app store: docker.io, quay.io. Unit 6 · Containers
Regulatory domain A country's radio rules, chosen with the country setting: legal channels, DFS and maximum power. Unit 3 · Lab 05-01 · Wireless basics and your radio name
Relative path An address that starts from where you stand, like "the second door on the left". Unit 4 · Terminal survival and the directory tree
Relative reference A cell reference that moves when you copy the formula. Unit 7 · Office and collaborative tools
Release channel The speed lane of updates a router follows: long-term, stable, testing or development. Unit 3 · Lab 01-03 · Packages, release channels and upgrades
Release upgrade Moving a whole system to its next version (Debian 12 → 13, Windows 10 → 11). A planned job, with a way back. Unit 2 · Software and updates on Windows
Remote Another copy of your repository somewhere else, known by a short name, usually origin. Unit 7 · Git remotes and collaboration
Remote connection virt-manager talking to libvirt on another machine over SSH: your PC is the remote control, the VM runs over there. Unit 2 · Your first VM
Remote desktop A far machine's screen on yours, with your mouse and keyboard acting there: sitting on its chair from far away. Unit 6 · Remote desktop
Repeater One radio that is a station of an AP and an AP of its own: no cables, but half the speed. Unit 3 · Lab 05-03 · Your own access point
reply-only (ARP) An ARP mode where the router stops adding dynamic entries: the concierge only uses the residents list. Not a firewall. Unit 3 · Lab 02-03 · Static ARP
Repository A warehouse of packages on a server, run by the distribution — the kitchen's wholesale supplier. Unit 2 · Package managers
requirements.txt The shopping list of a Python project: every package with its exact version, to rebuild the environment anywhere. Unit 5 · Dependencies and isolated environments
Reservation A DHCP rule "this MAC always gets this address". Unit 3 · DHCP and DNS
Reset configuration Erases the router's configuration and reboots it. Unit 3 · Lab 01-06 · Backup, reset and restore
Resolver The DNS server your PC asks; it walks the tree and caches the answers. Unit 3 · DHCP and DNS
Resource Anything useful a computer can offer: files, a printer, a program, a shell. Unit 6 · Clients, servers and shared resources
restic A free backup program that keeps encrypted, deduplicated snapshots in a repository. Unit 4 · restic and the restore drill
Restore drill Rehearsing a recovery against the clock, like a fire drill for data. Unit 4 · restic and the restore drill
Restore point A saved copy of Windows' system files, programs and settings at one moment. It never touches your documents. Unit 2 · Snapshots and recovery
Retail licence Bought on its own; can be moved to another computer, one at a time. Unit 2 · Software licences
Retrieval practice Trying to remember before you look; it makes things stick better than re-reading. Unit 5 · Sysadmin cheat sheet
RFC One of the public documents where the Internet's rules are written. Unit 3 · How a message travels
Ring 0 / ring 3 Intel and AMD names for kernel mode and user mode. Unit 2 · OS architecture
RIPE NCC Europe's regional address registry; its last IPv4 addresses went on 25 November 2019. Unit 3 · NAT and Internet access
Risk How likely × how bad. Unit 6 · Why protect systems
RJ45 (8P8C) The network cable plug: 8 positions, 8 contacts. Unit 3 · Cabling a LAN
Roaming A device moving between several APs that announce the same SSID. Unit 3 · Wireless LAN
robocopy "Robust copy", the Windows folder-copy tool; /MIR mirrors like rsync --delete; exit code 1 = success. Unit 4 · Scheduling tasks
Rogue DHCP server A second, unwanted DHCP server that hands out wrong settings. Unit 3 · DHCP and DNS
ROM Read-Only Memory — non-volatile memory written once and then only read. Its modern descendant is flash. Unit 1 · Memory
Root The all-powerful user on Linux: holds the master key to every room. Unit 2 · Ubuntu Server and first steps
Root partition (/) The partition that holds the system and, in a simple plan, everything else. Unit 2 · Planning an installation
Root server The top of the DNS tree (13 names, a to m.root-servers.net) Unit 3 · DHCP and DNS
Root squash NFS turning the client's root (UID 0) into nobody; on by default. Unit 6 · NFS
Route One line of the routing table: a destination network and the gateway that leads there. Unit 3 · Lab 04-01 · The default route
Route flags The letters before each route (D dynamic, A active, c connected, s static, I inactive, + ECMP). Unit 3 · Lab 04-01 · The default route
Router A computer whose job is passing information between networks — at home it connects your LAN to the Internet. Unit 1 · Hardware
Router Advertisement The message an IPv6 router sends to everyone on the link announcing the network prefix and itself as the way out. Unit 3 · IPv6 in 55 minutes
Router on a stick One router with one trunk cable and a VLAN interface (leg) per VLAN, routing between them. Unit 3 · VLANs
RouterBOARD MikroTik's own router hardware, which runs RouterOS. Unit 3 · Lab 01-01 · Getting in
RouterBOOT The small firmware that starts RouterOS on a RouterBOARD, like a PC's BIOS; upgrade it after RouterOS. Unit 3 · Lab 01-03 · Packages, release channels and upgrades
RouterOS MikroTik's operating system for routers, built on the Linux kernel. Unit 3 · Meet RouterOS
Routing Choosing where to send a packet next, junction after junction, until it arrives. Unit 3 · Routing
Routing table A device's signpost: each line says "for this network, go that way". Unit 3 · Routing
RPM Revolutions per minute — how fast an HDD's platters spin (5,400, 7,200, up to 15,000). Unit 1 · Storage
RPO Recovery point objective: how much work you may lose; set by how often you back up. Unit 4 · restic and the restore drill
RSAT Remote Server Administration Tools: Windows consoles to manage a domain from a client. Unit 6 · Domain users, groups and OUs
rsync Copies a folder sending only the differences; --delete makes the copy identical. Unit 4 · Backups
RTO Recovery time objective: how long you may be stopped; set by how fast you can restore. Unit 4 · restic and the restore drill
RTOS Real-time operating system: guarantees an answer within a fixed time, always (an airbag) Unit 2 · Comparing OSes
RTT Round-trip time: how long a ping takes to come back. Unit 3 · Lab 09-02 · Ping and Netwatch
Rule counters The packet and byte counts on every firewall rule, which prove that traffic really matched it. Unit 3 · Lab 06-01 · The input chain
Running / saved configuration Settings in RAM (gone after a reboot, ip) versus settings in a file (NetworkManager, Windows Settings) Unit 3 · Configuring TCP/IP on hosts
Runtime What must be on a machine for a finished program to run: the oven without which the dish cannot be served. Unit 5 · What a development machine needs

S

Term What it means Where you met it
SaaS Software as a Service: it runs on the provider's computers and you rent access; a way of delivering, not a licence. Unit 7 · Software by licence and purpose
SAE WPA3's handshake; a recording of it cannot be used to guess passwords offline. Unit 3 · Wireless LAN
Safe Mode Windows started with only the basic drivers and no extra programs, so you can find and fix a problem. Unit 2 · Snapshots and recovery
Safe mode (RouterOS) Ctrl+X in RouterOS: if your session dies, every change since you pressed it is undone automatically. Unit 3 · Lab 01-01 · Getting in
Salt A random value per account mixed into the password before hashing, so equal passwords give different hashes. Unit 5 · Account and password policies
SAM The Windows database where local accounts live; you only see it through tools, never as a text file. Unit 5 · Users and groups on Windows
Samba Free software (Andrew Tridgell, 1992) that makes Linux speak SMB. Unit 6 · Samba file server
Samba AD DC A free Active Directory domain controller made by Samba (since 4.0, 2012). Unit 6 · Domains and directory services
Sandbox A closed box that limits what an app can reach on your system. Flatpak and Snap use one. Unit 2 · Package managers
SATA Serial ATA — the cable interface designed for hard disks; caps any drive at ~550 MB/s. Unit 1 · Storage
Scan list The channels a station is allowed to listen on when it looks for APs. Unit 3 · Lab 05-02 · Connect list
Scheduler The part of the OS that says "switch!" and picks which process runs next. Unit 2 · What is an OS?
Scheduler (RouterOS) Runs RouterOS scripts at a set time or interval, like cron. Unit 3 · Lab 09-01 · E-mail from the router
Scope / target-scope Route numbers: scope says how close a route is, target-scope which routes may resolve its gateway. Unit 3 · Lab 04-05 · Recursive routing and failover
SCP Copies a file or folder over SSH in one line, like cp. Unit 7 · File transfer
Script A text file of commands that the shell runs top to bottom: a recipe card for the chef. Unit 4 · Shell scripts
SDK Software Development Kit: the full toolbox (compiler, libraries, tools) for one platform. Unit 5 · What a development machine needs
Search operator A word or symbol that filters search results: "...", site:, -word, filetype:, after:. Unit 7 · Finding technical documentation
Second factor A second proof besides the password, such as a code on your phone or a security key. Unit 5 · Account and password policies
Secure Boot UEFI feature that only runs bootloaders with a valid digital signature, blocking bootkits. Unit 1 · Boot
Secure desktop The dimmed screen of a UAC prompt, where only Windows itself can click. Unit 5 · Users and groups on Windows
Secure string A PowerShell way of holding a password so it is never stored as plain text. Unit 5 · Users and groups on Windows
Security policy The set of rules a system applies to everybody: passwords, rights, audit, sign-in notice. Unit 6 · User rights and security policies
Security profile Legacy wireless settings for WiFi security (mode, WPA2 PSK, ciphers, password) given to an interface. Unit 3 · Lab 05-03 · Your own access point
Segment The transport layer's unit when it uses TCP (with UDP it is a datagram) Unit 3 · How a message travels
Select-String PowerShell's grep: searches text in files and ignores case by default. Unit 5 · Bash and PowerShell side by side
Self-signed certificate A certificate its owner signed alone: it encrypts, but nobody trusted vouches for it. Unit 3 · SSH and TLS
Serial console A direct cable to the router's console port: no network, no IP needed. Unit 3 · Lab 01-01 · Getting in
Server A role, not a box: any computer that offers a service to others over the network. Unit 2 · Comparing OSes
Service A background program with no window and no user, started and watched by the system: the kitchen's dishwasher. Unit 5 · Services and systemd
Service (RouterOS) A program on the router waiting on a port (SSH 22, WinBox 8291...): a door to close if unused. Unit 3 · Lab 01-05 · Secure your router
Service name (PPPoE) A label a PPPoE server announces, to pick the right one when there are several. Unit 3 · Lab 08-01 · PPPoE client
Service ticket A Kerberos ticket for one service, shown to it instead of your password. Unit 6 · Domains and directory services
setgid A special bit (octal 2, s in the group's x); on a folder, the rubber stamp that gives every new file the folder's group. Unit 5 · Special permissions and ACL
setuid A special bit (octal 4, s in the owner's x) that makes a program run as its owner, not as you: how passwd writes in /etc/shadow. Unit 5 · Special permissions and ACL
sfc System File Checker: the Windows command that compares protected system files with a good copy and repairs them. Unit 5 · Maintenance and optimisation
SFTP SSH File Transfer Protocol: an interactive file session inside SSH, on port 22. Unit 7 · File transfer
SHA-256 A hash function giving 256 bits, written as 64 hex characters. Unit 2 · Verify an ISO
Share A folder of the server offered to the network under a name: one labelled drawer of the cabinet. Unit 6 · Samba file server
Share permissions Who may use a share and how, written in smb.conf; the file system still has the last word. Unit 6 · Share permissions and groups
Shebang The first line #!/bin/bash: tells the kernel which program must read the file. Unit 4 · Shell scripts
Shell An ordinary program that takes your orders and passes them to the kernel; graphical or command line. Unit 2 · OS architecture
Shell builtin A command that is part of Bash itself (like cd), with help instead of a man page. Unit 7 · Finding technical documentation
SID Security identifier: the number Windows really uses to identify an account, like the UID on Linux. Unit 5 · Users and groups on Windows
SIGKILL Signal 9: the kernel removes the process at once; it cannot save or clean up. Unit 5 · Processes
Signal A numbered message the kernel delivers to a process: SIGTERM asks politely, SIGKILL cannot be refused. Unit 5 · Processes
Signature The fingerprint of a known piece of malware that an antivirus looks for. Unit 6 · Basic security utilities
SIGTERM Signal 15, what kill PID sends: "please finish and leave". Unit 5 · Processes
Simple queue A speed limit for one target, with one value for upload and one for download. Unit 3 · Lab 07-01 · Simple queue
Site survey Measuring which networks are in the air, on which channels and how strong, before installing an AP. Unit 3 · Wireless LAN
Skin A JSON file that hides or simplifies WebFig and WinBox menus for a user group; not a security tool. Unit 3 · Lab 01-01 · Getting in
SLAAC Stateless Address Autoconfiguration: the router announces the street (the /64 prefix) and each PC picks its own house number. Unit 3 · IPv6 in 55 minutes
Slow path The normal way through a RouterOS bridge: the whole Linux network stack, where every feature can see the frame. Unit 3 · Lab 03-02 · Bridge performance
SmartScreen The Windows check that warns before you run an unknown or unsigned download. Unit 2 · Software and updates on Windows
SMB Server Message Block (IBM, 1983, TCP 445): the Windows file-sharing protocol. Unit 6 · Samba file server
SMT Simultaneous Multithreading (Intel: Hyper-Threading) — one core runs two threads, using the gaps while it waits for memory. Unit 1 · CPU
SMTP Simple Mail Transfer Protocol: the rules to hand a letter over, from client to server and server to server. Unit 7 · Email and messaging
Snap Canonical's package format, bundled with its dependencies and sandboxed; installed by default on Ubuntu. Unit 2 · Package managers
Snapshot The saved state of a VM's disk at one moment, to return to. An undo button, not a backup. Unit 2 · Snapshots and recovery
Sniffer A program that copies the packets passing by, so it can read every postcard. Unit 3 · SSH and TLS
SNMP Simple Network Management Protocol: a manager reads values from an agent on each device, over UDP 161. Unit 3 · Lab 09-05 · SNMP
Snooper The RouterOS tool that shows every AP and station on every channel: looking out of the window. Unit 3 · Lab 05-02 · Connect list
Socket The connector on the motherboard where the CPU sits. It must match the CPU family (e.g. AM4). Unit 1 · CPU
SO-DIMM Small Outline DIMM — the shorter RAM module used in laptops and mini PCs. Unit 1 · Memory
Software need One line saying who must be able to do what, marked must or should — the diagnosis before the prescription. Unit 7 · Software needs in real workplaces
Source code The program as text a person can read: the recipe. Unit 2 · Software licences
Source-available You can read the code, but the licence restricts what you do with it. Unit 7 · Software by licence and purpose
SPF / DKIM / DMARC Checks that the sending server is allowed to send for that domain. Unit 7 · Email and messaging
Spooler The program that keeps the print queue and feeds the printer. Unit 6 · Print server
Spreadsheet Squared paper where every square can be a calculator, wired to the others. Unit 7 · Office and collaborative tools
SRAM Static RAM — about 6 transistors per bit, no refresh, fast and expensive. Used for cache. Unit 1 · Memory
src-nat Source NAT: changes who a packet seems to come from, so a private LAN can use the router's address. Unit 3 · Lab 06-05 · Destination NAT
SRV record A DNS record that answers which host offers a service, and on which port. Unit 6 · Domains and directory services
SSD Solid State Drive — a disk with no moving parts, storing bits in flash memory chips. Much faster than an HDD. Unit 1 · Hardware
SSH The way to type commands on a server from another computer. Unit 2 · Virtualisation
SSH tunnel An SSH login that also carries one port across: localhost:8006 on your PC leads to a web page inside the server's private network. Unit 2 · Proxmox VE
SSID The network's name, the name written on the canteen table. Unit 3 · Wireless LAN
SSL The older name of TLS (Netscape, 1995); every SSL version is broken and forbidden today. Unit 3 · SSH and TLS
SSSD The Linux service that looks up domain users in the directory and checks their passwords with Kerberos. Unit 6 · Joining a domain
SSTP Secure Socket Tunneling Protocol (Microsoft): PPP inside TLS on tcp/443, so it looks like HTTPS. Unit 3 · Lab 08-03 · PPTP and SSTP
Staging area What will go into the next commit, chosen with git add: what you place in front of the camera. Unit 7 · Git basics
Standard user A Windows account in the group Users, with no administrator rights. Unit 5 · Users and groups on Windows
Startup type Windows setting for a service at boot: Automatic, Automatic (Delayed Start), Manual, Disabled. Unit 5 · Services and systemd
Stateful firewall A firewall that remembers conversations (new, established, related) so answers can come back. Unit 3 · Ports and firewalls
Static ARP entry An IP → MAC pair written by hand in the ARP table: a name on the list. Unit 3 · Lab 02-03 · Static ARP
Static DNS entry A name → address pair typed into the router's own DNS server. Unit 3 · Lab 02-01 · DHCP server
Static IP address An address that never changes, so clients always find the server. Unit 6 · Clients, servers and shared resources
Static lease A DHCP reservation: the PC still asks by DHCP, but its MAC always gets the same address. Unit 3 · Wired LAN with RouterOS
Static route A route typed by a person: "for this network, hand it to that gateway". Unit 3 · Routing
static-only A DHCP pool setting that hands out addresses only to devices with a static lease. Unit 3 · Lab 02-02 · Static DHCP leases
Station A WiFi client that joins an access point: your phone, your laptop, a router in station mode. Unit 3 · Lab 05-01 · Wireless basics and your radio name
Station bridge The wireless way to bridge a RouterOS station to a RouterOS AP when no cable is available. Unit 3 · Lab 03-01 · Bridge
stderr Standard error, stream 2: a command's error messages; it reaches the screen by its own pipe. Unit 5 · Back to the shell
stdin Standard input, stream 0: what a command reads, the keyboard by default. Unit 5 · Back to the shell
stdout Standard output, stream 1: a command's results, the screen by default. Unit 5 · Back to the shell
Sticky bit A special bit (octal 1, t in the others' x); in a shared folder you may only delete your own files, like in /tmp. Unit 5 · Special permissions and ACL
Storage The non-volatile part of the computer that keeps data with the power off — the kitchen's pantry. Unit 1 · Storage
Stored-program concept The program lives in the same memory as the data, both stored as bits. The 1945 revolution: no more rewiring machines to reprogram them. Unit 1 · Hardware
strace A tool that runs a program and prints every system call it makes. Unit 2 · OS architecture
Straight-through / crossover cable Same order on both ends versus A on one end and B on the other. Unit 3 · Cabling a LAN
Stream One of the three channels of a command: stdin (0) in, stdout (1) results out, stderr (2) complaints out. Unit 5 · Back to the shell
su Opens a session as another user, with that user's password. Unit 5 · Users and groups on Linux
Subnet A smaller network cut from a bigger one, with its own network and broadcast address: a shorter street. Unit 3 · Subnetting
Subnet mask 32 bits, ones over the network part and zeros over the host part: where the street ends. Unit 3 · IPv4 addressing
sudo Borrow root's master key for one command, after typing your own password. Unit 2 · Ubuntu Server and first steps
sudoers The file /etc/sudoers (plus /etc/sudoers.d/) where sudo reads who may run what, as whom. Unit 5 · sudo and least privilege
SUMIF / COUNTIF Functions that add or count only the cells that meet a condition. Unit 7 · Office and collaborative tools
SUMPRODUCT Multiplies two ranges pair by pair and adds the results: a selection matrix in one formula. Unit 7 · Office and collaborative tools
supout.rif The complete check-up file MikroTik support asks for; the watchdog can write an autosupout.rif after a crash. Unit 3 · Lab 09-07 · Logs, supout.rif and documenting the router
Supplementary group Any extra group a user belongs to, such as a department. Unit 5 · Users and groups on Linux
Swap Disk space the OS uses as overflow when RAM is full (Windows: page file). Much slower than RAM. Unit 1 · Memory
Switch Delivers messages inside one LAN to the right device, using MAC addresses — the building's concierge. Unit 1 · Networks
swtpm A program on the host that behaves like a TPM chip, so a VM gets an emulated TPM. Unit 2 · Installing Windows 11
Symbolic notation Permissions written as who/what/which: u+x, g-w, o=. Unit 5 · Linux permissions
Syslog The Unix logging system Eric Allman wrote for sendmail in the early 1980s; it gave us the 8 severity levels. Unit 5 · Logs and journald
System account An account for a service, not a person (UID 1–999, shell nologin) Unit 5 · Users and groups on Linux
System call A program ringing the bell at the hatch: a request to the kernel ("open this file") Unit 2 · OS architecture
System Protection The Windows setting that allows restore points. Off by default on Windows 11. Unit 2 · Snapshots and recovery
System software Programs that run the machine itself (the OS, drivers, firmware), not a job for the user. Unit 2 · What is an OS?
systemctl The command that talks to systemd: status, start, stop, enable, disable. Unit 5 · Services and systemd
systemd PID 1 on Debian: the kitchen's shift manager that starts, watches and restarts services. Unit 5 · Services and systemd
systemd timer A .timer unit that starts a .service unit on a schedule; can catch up missed runs. Unit 4 · Scheduling tasks

T

Term What it means Where you met it
T568B The standard wire order in almost every patch cable: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. Unit 3 · Cabling a LAN
Tag (image)** The version part of an image name (nginx:1.30); latest changes without warning. Unit 6 · Containers
tar Packs many files into one archive (tape archive); z adds gzip compression. Unit 4 · Backups
Target (queue) Whose traffic a simple queue limits: an address, a network or an interface. Unit 3 · Lab 07-01 · Simple queue
Task Scheduler The Windows scheduler: each task is a trigger plus an action. Unit 4 · Scheduling tasks
TCO Total cost of ownership: licences plus the hours of installation, migration, training and support, counted over years. Unit 7 · Software needs in real workplaces
TCP Transmission Control Protocol: sets up a connection and resends what is lost, like a phone call. Unit 3 · Ports and firewalls
tcpdump A text program that prints every message passing through a network card. Unit 3 · How a message travels
TCP/IP model The practical cousin of the OSI model: 4 layers instead of 7. It is the model the Internet actually runs on. Unit 1 · Networking
TDP Thermal Design Power — the heat, in watts, the cooler must remove under sustained load. Unit 1 · CPU
Team messaging Short messages grouped in channels, threads, mentions and direct messages. Unit 7 · Email and messaging
Technical documentation Any written explanation of how a program or system works: manuals, help texts, wikis, guides. Unit 7 · Finding technical documentation
Telnet The old way to type commands on a remote machine (1983, TCP port 23); it sends everything, password included, as a readable postcard. Unit 3 · SSH and TLS
Template A ready-made small system in one compressed file, used to create containers with no installer. Unit 2 · Proxmox VE
Terminal The window where you type commands for the shell; called a tty after the old teletypewriters. Unit 4 · Terminal survival and the directory tree
TGT Ticket-granting ticket: the wristband you get from the KDC, used to ask for service tickets. Unit 6 · Domains and directory services
The Dude MikroTik's free monitoring tool: it finds devices, draws them on a map and raises alerts when they fail. Unit 3 · Lab 09-06 · The Dude
Thermal throttling A CPU lowering its clock to protect itself when it gets too hot. Unit 1 · CPU
Thin provisioning The guest sees the full disk; the host stores only what was written. Unit 2 · Your first VM
Thread One sequence of instructions being run; with SMT a core juggles two. Unit 1 · CPU
Threat Whatever could cause harm: a thief, a fire, a clumsy cook. Unit 6 · Why protect systems
Three-way handshake SYN, SYN-ACK, ACK: how TCP opens a connection. Unit 3 · Ports and firewalls
Ticket The written record of a fault: symptom, evidence, cause and fix. Unit 3 · Network troubleshooting
Time slice The few milliseconds a process gets on a core before the scheduler switches. Unit 2 · What is an OS?
Time zone A rule to show UTC as local time, named Region/City like Europe/Madrid. Unit 5 · Configuring the system by command
TLD Top-level domain: the last label of a name (org, com, es) Unit 3 · DHCP and DNS
TLS Transport Layer Security, the sealed envelope of the web and many apps; TLS 1.3 (2018) is the current version. Unit 3 · SSH and TLS
Toolchain The set of tools needed to build a program, e.g. the JDK plus Git. Unit 5 · What a development machine needs
Topology The shape of a network: bus, star, ring or mesh. Almost every LAN today is a star. Unit 1 · Networks
Torch RouterOS's real-time microscope: every flow crossing an interface right now, with its speed. Unit 3 · Lab 07-01 · Simple queue
TPM Trusted Platform Module: a small security chip (or CPU function) that keeps secret keys; Windows 11 needs version 2.0. Unit 2 · Comparing OSes
traceroute Tool that lists one line per router on the way to a destination (tracert on Windows) Unit 3 · Routing
Traffic monitor RouterOS's heart-rate monitor: how much is flowing through one port right now. Unit 3 · Lab 09-03 · The toolbox
Transistor A tiny electronic switch, on or off: the physical home of a bit. CPUs have billions. Unit 1 · CPU
Translation table The receptionist's notebook: which public port belongs to which private address (connection tracking) Unit 3 · NAT and Internet access
Transparent bridge A router turned into a bridge between its Internet and LAN ports: it rewrites nothing, so nobody notices it. Unit 3 · Lab 03-01 · Bridge
Transparent proxy A proxy the client never configured and does not know is there. Unit 3 · Lab 06-06 · Redirect
Trigger In Task Scheduler, the condition that starts a task (a time, a log on...) Unit 4 · Scheduling tasks
TRIM The message telling an SSD which blocks are free, so it can erase them in advance. Unit 5 · Maintenance and optimisation
Triplet A group of three permission letters (rwx) for the owner, the group or others. Unit 5 · Linux permissions
Troubleshooting Finding the cause of a fault with a method, proving it with evidence, and fixing it. Unit 3 · Network troubleshooting
Trunk port A switch port that carries several VLANs, tagged, to another switch, router or AP. Unit 3 · VLANs
TTL A counter in the IP header that each router lowers by one; in DNS, how long an answer may be cached. Unit 3 · Wireshark: first capture
Tunnel The path a VPN builds between its two ends, over the network you already have. Unit 3 · VPN with WireGuard
Turing machine Alan Turing's 1936 imaginary computer: an endless tape, a head that reads and writes one cell at a time, and a table of rules. Anything computable can be computed by one. Unit 1 · Hardware
Turing-complete Able to simulate any Turing machine — the mathematical meaning of "is a computer". Real computers only get close, because their memory is finite. Unit 1 · Hardware
Twisted pair The usual network cable: 8 copper wires in 4 twisted pairs, RJ45 connector, max 100 m. Unit 1 · Networks
Type 1 hypervisor Bare metal: runs directly on the hardware (ESXi, Hyper-V, Proxmox VE) Unit 2 · Virtualisation
Type 2 hypervisor Hosted: runs as an app on a normal OS (VirtualBox) Unit 2 · Virtualisation
Typesetting Laying out text on pages: margins, fonts, numbered headings, contents. Unit 7 · Docs as code
Typst A typesetting program that lays out text on pages and produces a PDF. Unit 7 · Docs as code
tz database The list of every time zone rule on Earth, kept by volunteers since 1986 and published by IANA. Unit 5 · Configuring the system by command

U

Term What it means Where you met it
UAC User Account Control: the dimmed screen where Windows asks for administrator rights — Windows' cousin of sudo. Unit 2 · Software and updates on Windows
Ubuntu Canonical's operating system (2004), built from Debian, with a release every six months and an LTS every two years. Unit 2 · Ubuntu Server and first steps
UDP User Datagram Protocol: just sends, no guarantees, like a postcard. Unit 3 · Ports and firewalls
UEFI Unified Extensible Firmware Interface — modern firmware that replaced BIOS: GPT disks, ESP boot files, Secure Boot. Unit 1 · Boot
ufw Uncomplicated firewall: Ubuntu/Debian's simple front end to the kernel's packet filter. Unit 3 · Ports and firewalls
UID User identifier: the number on the cook's apron; the system reads it, not your name. Unit 5 · Users and groups on Linux
umask The permissions taken away from every new file (from 666) and directory (from 777) Unit 5 · Linux permissions
Unattended-upgrades The Ubuntu service that installs security updates by itself every day. Unit 2 · Software and updates on Windows
UNC path The Windows address of a share: \server\share. Unit 6 · Samba file server
Unique local address A private IPv6 address starting with fc or fd, like 10.x.x.x in IPv4. Unit 3 · IPv6 in 55 minutes
Unit / unit file Anything systemd manages, described by a small text file with [Unit], [Service] and [Install] sections. Unit 5 · Services and systemd
Unit (systemd) A small text file that describes something systemd manages: a service, a timer... Unit 4 · Scheduling tasks
Untracked A file Git can see but does not follow yet, because it was never added. Unit 7 · Git basics
Untracked (connection) The connection state of a packet a raw rule told connection tracking to ignore. Unit 3 · Lab 06-08 · Connection tracking
UPN User principal name: a domain account written like an e-mail address, marta@tramuntana.internal. Unit 6 · Joining a domain
Upstream The remote branch your local branch is linked to, set once with git push -u. Unit 7 · Git remotes and collaboration
USB Universal Serial Bus (1996) — the universal door for peripherals. The version sets the speed (12 Mbit/s to 80 Gbit/s); the connector (A, B, C) is only the shape. Unit 1 · Peripherals
Use IP Firewall A bridge setting that sends bridged traffic through the IP firewall too, and down the slow path. Unit 3 · Lab 03-02 · Bridge performance
User account A number the system uses to tell people and programs apart, plus a name, home and shell for humans. Unit 5 · Users and groups on Linux
User group (RouterOS) The group every RouterOS user belongs to; its policies say what its members may do. Unit 3 · Lab 01-05 · Secure your router
User mode The CPU's front room: a program may only use its own memory and must ask for everything else. Unit 2 · OS architecture
User right Who may do an action on the whole computer (log in, shut down, change the time): your staff pass, not a key. Unit 6 · User rights and security policies
useradd The bare tool under adduser: no home and no password unless told. Unit 5 · Users and groups on Linux
usermod Changes an existing user; -aG adds groups, -G alone replaces them. Unit 5 · Users and groups on Linux
UTC Coordinated Universal Time: the one clock for the whole planet that the kernel counts in, with no summer time. Unit 5 · Configuring the system by command
UTP Unshielded twisted pair: 8 copper wires in 4 twisted pairs, no shield. Unit 3 · Cabling a LAN
UUID A random identifier written into a file system when it is created; it travels with it, unlike /dev/vdb1. Unit 4 · File systems

V

Term What it means Where you met it
Variable A box with a name that holds a value: name="Marta", read with $name. Unit 4 · Shell scripts
vCPU A virtual processor: turns on a real core, lent by the host. Unit 2 · Virtualisation
Version control A program that keeps the history of a folder: every saved state, who saved it, when and why. Unit 7 · Git basics
Version history The record a shared document keeps of every change and who made it. Unit 7 · Office and collaborative tools
Viewer / Commenter / Editor The three sharing roles: read, read and comment, change. Unit 7 · Office and collaborative tools
VirtIO A kind of virtual device made for VMs, faster than imitating real hardware. Linux has its drivers built in; Windows needs them from a CD. Unit 2 · Installing Windows 11
virt-manager The window you click in to manage VMs; it gives orders to libvirt. Unit 2 · Virtualisation
Virtual disk A VM's disk, which on the host is just a file. Unit 2 · Virtualisation
Virtual environment A folder with a project's own Python libraries, switched on by putting its bin first in PATH: a private shelf per dish. Unit 5 · Dependencies and isolated environments
Virtual machine (VM)** A computer made of software, running inside a real one: one brand in the shared kitchen. Unit 2 · Virtualisation
visudo The safe way to edit the sudo rules: it checks the grammar before saving. Unit 5 · sudo and least privilege
VLAN Virtual LAN: one switch behaving as several, each its own broadcast domain and subnet. Unit 3 · VLANs
VLAN ID The 12-bit number in the 802.1Q tag that says which VLAN a frame belongs to (1 to 4094) Unit 3 · VLANs
VNC Virtual Network Computing (Cambridge, 1998, port 5900): shows the screen that is in use. Unit 6 · Remote desktop
Volatile Memory that empties when the power is cut — RAM. Unit 1 · Hardware
Volume Windows' word for a partition with a file system it can use, usually with a drive letter. Unit 4 · Windows Disk Management
Volume group (VG) The pool that joins all the physical volumes: the binder itself. Unit 4 · LVM and RAID
Volume licence One agreement covering many computers in an organisation. Unit 2 · Software licences
Von Neumann architecture The 1945 blueprint almost every computer still uses: CPU + memory + I/O, connected by a bus, with the program stored in memory as bits. Unit 1 · Hardware
Von Neumann bottleneck The one-corridor problem: the CPU is faster than RAM, so it ends up waiting at the bus for data to arrive. Cache exists to fight this. Unit 1 · Hardware
VPN Virtual private network: private packets carried, encrypted, inside ordinary packets, like an envelope inside an envelope. Unit 3 · VPN with WireGuard
VT-x / AMD-V The CPU features (Intel / AMD) that let a hypervisor run guests on the real CPU; can be switched off in the firmware. Unit 2 · Virtualisation
Vulnerability The weak point a threat would use: the back door that does not lock. Unit 6 · Why protect systems

W

Term What it means Where you met it
WAN Wide Area Network — many LANs connected across long distances. The Internet is the biggest WAN there is. Unit 1 · Networking
WAN / LAN port The router port towards the outside world versus the ports towards your own network. Unit 3 · Meet RouterOS
Watchdog The RouterOS guard that notices a crash and can write an autosupout.rif by itself. Unit 3 · Lab 09-07 · Logs, supout.rif and documenting the router
WebFig RouterOS's web interface, at the router's address in a browser. Unit 3 · Meet RouterOS
Weighted selection matrix A table that scores candidates on criteria, multiplies by how much each criterion matters and adds it up. Unit 7 · Software needs in real workplaces
Well-known ports Ports 0–1023, fixed numbers for system services (SSH 22, DNS 53, HTTP 80, HTTPS 443) Unit 3 · Ports and firewalls
White label The same product sold under someone else's brand: same factory, different box. Unit 3 · Lab 01-04 · Your own brand
Wi-Fi Alliance The industry group that certifies Wi-Fi devices and introduced the Wi-Fi ⅘/6 names in 2018. Unit 3 · Wireless LAN
WiFi 4 / 5 / 6 / 7 Friendly names for 802.11n, ac, ax and be. Unit 3 · Lab 05-01 · Wireless basics and your radio name
wifi-qcom / wireless The RouterOS packages that drive the radio: wifi-qcom for the new WiFi menu, wireless for the legacy one. Unit 3 · Lab 05-01 · Wireless basics and your radio name
Wildcard A character that stands for others (*, ?, [1-3]), expanded by the shell before the command runs. Unit 4 · Finding information
WinBox MikroTik's program to manage a router; it can connect by MAC address. Unit 3 · Meet RouterOS
Windows NT The kernel family under Windows 10, Windows 11 and Windows Server. Unit 2 · Comparing OSes
Windows Update The part of Windows that downloads and installs updates for Windows and Microsoft products. Unit 2 · Software and updates on Windows
winget The package manager of Windows (2020): search, install, upgrade and uninstall programs from the Terminal. Unit 2 · Software and updates on Windows
WinRE Windows Recovery Environment: a tiny second Windows on its own partition, for repairs when the big one cannot start. Unit 2 · Snapshots and recovery
WireGuard A small, modern VPN (Jason A. Donenfeld, 2016) over UDP; in Linux since 5.6 and in RouterOS v7. Unit 3 · VPN with WireGuard
Wireshark The free graphical packet analyser (born Ethereal, 1998) Unit 3 · Wireshark: first capture
Word processor The office program for writing letters and reports. Unit 7 · Office and collaborative tools
Workgroup Computers where each one keeps its own list of accounts. Unit 6 · Domains and directory services
Working directory Your project files as they are right now: the room where things move around. Unit 7 · Git basics
Worm Malware that spreads by itself from machine to machine, with no click. Unit 6 · Why protect systems
WPA2 / WPA3 The Wi-Fi security standards acceptable today (2004 / 2018); WEP and WPA are broken. Unit 3 · Wireless LAN
WPS WiFi Protected Setup: press a button on the AP and on the device, and the AP hands over the password. Unit 3 · Lab 05-04 · WPS
WPS PIN WPS's 8-digit sticker code; guessable in 11,000 tries, so RouterOS does not support it. Unit 3 · Lab 05-04 · WPS

X

Term What it means Where you met it
XFS A Linux file system for very large files and disks (1993, Silicon Graphics); can grow but not shrink. Unit 4 · File systems
XML Plain text with tags, a cousin of HTML. Unit 7 · Office and collaborative tools
XNU Apple's kernel, under macOS, iOS, iPadOS and watchOS. Unit 2 · Comparing OSes

Y

Term What it means Where you met it
YAML A text format where indentation with spaces is the structure; used by Netplan and compose files. Unit 6 · Composing services
yescrypt The hashing method Debian uses for passwords (default since Debian 11); its hashes start with \(y\). Unit 5 · Users and groups on Linux

Z

Term What it means Where you met it
ZIP A popular lossless compression format: the original file comes back exactly, bit for bit. Unit 1 · Data
ZIP archive A box of compressed files packed into one. Unit 7 · Office and collaborative tools
zstd Zstandard (2016): a modern compressor, almost as small as xz and much faster. Unit 4 · Compression, encryption, integrity