A–Z tech glossary
258 networking, cybersecurity and cloud terms explained in one plain-English line each. Follow "Read the note" for the full explanation.
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- 5G
- The fifth generation of mobile networks, offering higher speeds, lower latency and support for many more connected devices. Read the note
- 802.1Q
- The standard for VLAN tagging: it adds a small tag to Ethernet frames so a trunk can carry many VLANs. Read the note
- 802.1X
- Port-based network access control: a device must authenticate (usually via RADIUS) before it can use a switch port or Wi-Fi. Read the note
A
- AAA
- Authentication, authorisation and accounting: who you are, what you may do, and a record of what you did. Read the note
- Access control list (ACL)
- An ordered list of permit and deny rules that filters traffic on a router, switch or firewall. Read the note
- Access point (AP)
- A device that connects Wi-Fi clients to a wired network. Read the note
- Active Directory (AD)
- Microsoft’s directory service that stores users, computers and groups and controls sign-in on a Windows network. Read the note
- Administrative distance
- How much a router trusts a source of routing information; the lower value wins when two sources offer the same route. Read the note
- AES
- Advanced Encryption Standard: the most widely used symmetric encryption algorithm, with 128-, 192- or 256-bit keys. Read the note
- Air gap
- Keeping a system physically separated from other networks so it cannot be reached remotely. Read the note
- Ansible
- An agentless automation tool that configures servers and network devices using simple YAML playbooks. Read the note
- Antivirus
- Software that detects and removes known malware on a device, mostly by matching signatures and behaviour. Read the note
- API
- Application programming interface: a defined way for one program to ask another for data or actions. Read the note
- APIPA
- Automatic Private IP Addressing: the 169.254.x.x address Windows gives itself when no DHCP server answers. Read the note
- ARP
- Address Resolution Protocol: finds the MAC address that belongs to an IPv4 address on the local network. Read the note
- Attack surface
- All the points where an attacker could try to get in: devices, services, accounts, apps and people. Read the note
- Authentication
- Proving who you are, for example with a password, a security key or a fingerprint. Read the note
- Authorisation
- Deciding what an authenticated user or system is allowed to do. Read the note
- Availability
- Making sure systems and data are there when people need them; one part of the CIA triad. Read the note
- AWS
- Amazon Web Services: Amazon’s cloud platform offering computing, storage, networking and many other services. Read the note
- Azure
- Microsoft’s cloud platform, closely linked with Microsoft 365 and Entra ID. Read the note
B
- Backdoor
- A hidden way into a system that bypasses normal security, often left by malware or an attacker. Read the note
- Backup
- A copy of data kept separately so it can be restored after loss, failure or ransomware. Read the note
- Bandwidth
- The maximum amount of data a link can carry per second, measured in bits per second. Read the note
- Bash
- The command shell used on most Linux systems, also used to write scripts. Read the note
- BGP
- Border Gateway Protocol: the routing protocol that connects networks across the internet. Read the note
- Binary
- The base-2 number system of 0s and 1s that computers use, and the key to understanding subnet masks. Read the note
- Biometrics
- Using a physical trait such as a fingerprint or face to prove identity. Read the note
- Blockchain
- A shared, append-only record of transactions kept in sync across many computers. Read the note
- Bluetooth Low Energy (BLE)
- A low-power wireless technology used by wearables, trackers and many IoT devices. Read the note
- Botnet
- A network of infected devices controlled by an attacker, often used for DDoS attacks or spam. Read the note
- BPDU Guard
- A switch feature that shuts a port if another switch is plugged in, protecting Spanning Tree. Read the note
- Broadcast
- A message sent to every device on the local network. Read the note
- Broadcast domain
- The group of devices that receive each other’s broadcasts; routers and VLANs separate them. Read the note
- Brute-force attack
- Guessing a password or key by trying many possibilities until one works. Read the note
- Business continuity
- Planning so an organisation can keep working during and after a disruption. Read the note
C
- Certificate
- A digital document, signed by a certificate authority, that links a public key to a website or organisation. Read the note
- Certificate authority (CA)
- A trusted organisation that checks identities and signs digital certificates. Read the note
- CIA triad
- Confidentiality, integrity and availability: the three core goals of information security. Read the note
- CIDR
- Classless Inter-Domain Routing: writing a network with a prefix length, such as 192.168.1.0/24. Read the note
- Cipher
- An algorithm used to encrypt and decrypt data. Read the note
- Cloud computing
- Using computing power, storage and software over the internet from a provider, paying for what you use. Read the note
- CoAP
- Constrained Application Protocol: a lightweight web-style protocol for small IoT devices. Read the note
- Collision domain
- A network segment where devices can interfere with each other’s transmissions; switches give each port its own. Read the note
- Confidentiality
- Keeping information private so only authorised people can read it; one part of the CIA triad. Read the note
- Container
- A lightweight, packaged application that runs with everything it needs, sharing the host’s operating system. Read the note
- Credential stuffing
- Trying usernames and passwords leaked from one site on many other sites. Read the note
- Cryptography
- The science of protecting information with codes, encryption, hashing and signatures. Read the note
- CSPM
- Cloud security posture management: tools that check cloud settings for risky misconfigurations. Read the note
- CVE
- Common Vulnerabilities and Exposures: the public ID system for known security flaws, such as CVE-2026-12345. Read the note
- CVSS
- Common Vulnerability Scoring System: a 0–10 score for how severe a vulnerability is. Read the note
- Cyber threat intelligence (CTI)
- Information about attackers, their tools and methods, used to make better defence decisions. Read the note
D
- Data centre
- A building or room full of servers, storage and network equipment that runs an organisation’s systems. Read the note
- Data loss prevention (DLP)
- Tools and rules that stop sensitive data leaving the organisation by mistake or on purpose. Read the note
- DDoS
- Distributed denial of service: flooding a service with traffic from many devices so real users cannot reach it. Read the note
- Default gateway
- The router a device sends traffic to when the destination is on another network. Read the note
- Defence in depth
- Using several layers of security so that if one fails, others still protect you. Read the note
- DHCP
- Dynamic Host Configuration Protocol: automatically gives devices an IP address, mask, gateway and DNS server. Read the note
- DHCP snooping
- A switch feature that blocks fake DHCP servers on user ports. Read the note
- Digital forensics
- Collecting and analysing digital evidence in a way that can be trusted, for example in court. Read the note
- Digital signature
- A cryptographic stamp that proves who created data and that it has not been changed. Read the note
- Digital twin
- A live digital model of a real device or system, used for monitoring and testing. Read the note
- Disaster recovery (DR)
- The plans and systems used to restore IT after a major failure. Read the note
- DMZ
- A separate network zone for public-facing servers, kept apart from the internal network. Read the note
- DNS
- Domain Name System: translates names like fmtechub.com into IP addresses. Read the note
- Docker
- A popular platform for building and running containers. Read the note
- DSCP
- A value in the IP header used by QoS to mark how important a packet is. Read the note
- Dynamic ARP Inspection (DAI)
- A switch feature that checks ARP messages to stop ARP spoofing. Read the note
E
- Edge computing
- Processing data close to where it is produced instead of in a distant data centre. Read the note
- EDR
- Endpoint detection and response: software that watches devices for suspicious behaviour and helps respond to attacks. Read the note
- EIGRP
- Enhanced Interior Gateway Routing Protocol: an advanced distance-vector routing protocol developed by Cisco. Read the note
- Encryption
- Scrambling data with a key so only someone with the right key can read it. Read the note
- Endpoint
- Any device that connects to a network, such as a laptop, phone, server or printer. Read the note
- Entra ID
- Microsoft’s cloud identity service (formerly Azure Active Directory) used to sign in to Microsoft 365 and Azure. Read the note
- EtherChannel
- Bundling several physical links between switches into one logical link for more bandwidth and redundancy. Read the note
- Ethernet
- The standard technology for wired local networks. Read the note
- Exploit
- Code or a technique that takes advantage of a vulnerability. Read the note
F
- FHRP
- First hop redundancy protocol, such as HSRP or VRRP: gives hosts a backup default gateway. Read the note
- Fibre optic
- Cable that carries data as light, used for long distances and high speeds. Read the note
- Firewall
- A device or software that allows or blocks network traffic based on rules. Read the note
- Firmware
- The low-level software built into hardware such as routers, cameras and IoT devices. Read the note
- Frame
- A unit of data at Layer 2, with source and destination MAC addresses. Read the note
- Full duplex
- Sending and receiving at the same time on a link. Read the note
G
- Git
- A version control system that tracks changes to code and configuration files. Read the note
- GRE
- Generic Routing Encapsulation: a simple tunnel that carries packets between two routers. Read the note
H
- Hacker
- Someone who explores how systems work; ethical hackers do it with permission to improve security. Read the note
- Hardening
- Reducing a system’s attack surface by removing unneeded services and applying secure settings. Read the note
- Hash
- A fixed-length fingerprint of data; any change to the data changes the hash. Read the note
- Hexadecimal
- The base-16 number system (0–9 and A–F) used for MAC addresses, IPv6 and memory dumps. Read the note
- High availability (HA)
- Designing systems so they keep running even when a part fails. Read the note
- Honeypot
- A decoy system set up to attract attackers and study their behaviour. Read the note
- HSRP
- Hot Standby Router Protocol: Cisco’s way of sharing a virtual default gateway between routers. Read the note
- HTTP
- Hypertext Transfer Protocol: how web browsers and servers exchange web pages. Read the note
- HTTPS
- HTTP protected by TLS encryption, shown by the padlock in the browser. Read the note
- Hub
- An old network device that repeats every signal to every port; replaced by switches. Read the note
- Hybrid cloud
- Using a mix of on-premises systems and public cloud services together. Read the note
- Hypervisor
- Software that runs virtual machines on physical hardware. Read the note
I
- IaaS
- Infrastructure as a service: renting virtual servers, storage and networks from a cloud provider. Read the note
- IAM
- Identity and access management: controlling who can access what, and how. Read the note
- ICMP
- Internet Control Message Protocol: used by ping and traceroute to test and report network problems. Read the note
- IDS
- Intrusion detection system: watches traffic and alerts on suspicious activity. Read the note
- Incident response
- The organised way a team detects, contains and recovers from a security incident. Read the note
- Indicator of compromise (IoC)
- Evidence that a system may have been attacked, such as a malicious IP address or file hash. Read the note
- Infrastructure as code (IaC)
- Defining servers, networks and cloud resources in code files so they can be built automatically. Read the note
- Insider threat
- A risk from someone inside the organisation, whether malicious or careless. Read the note
- Integrity
- Making sure data is accurate and has not been changed without permission; one part of the CIA triad. Read the note
- IoT
- Internet of Things: everyday objects with sensors and network connections, such as smart meters and cameras. Read the note
- IP address
- The number that identifies a device on a network so data can be delivered to it. Read the note
- IPS
- Intrusion prevention system: like an IDS, but it can also block the suspicious traffic. Read the note
- IPsec
- A set of protocols that encrypt and authenticate IP traffic, commonly used for VPNs. Read the note
- IPv4
- Version 4 of the Internet Protocol, using 32-bit addresses such as 192.168.1.10. Read the note
- IPv6
- Version 6 of the Internet Protocol, using 128-bit addresses to solve the shortage of IPv4 addresses. Read the note
- IS-IS
- A link-state routing protocol often used inside large service provider networks. Read the note
J
- Jitter
- Variation in delay between packets, which causes choppy voice and video. Read the note
- JSON
- A simple text format for structured data, used by most web APIs. Read the note
K
- Kerberos
- A ticket-based authentication protocol used by Active Directory. Read the note
- Keylogger
- Malware or hardware that records the keys a person types to steal passwords. Read the note
- Key management
- Creating, storing, rotating and destroying encryption keys safely. Read the note
- Kubernetes
- A platform that runs and manages containers across many servers. Read the note
L
- LAN
- Local area network: a network in one home, office or building. Read the note
- Latency
- The delay for data to travel from source to destination, usually in milliseconds. Read the note
- Least privilege
- Giving people and systems only the access they need, and nothing more. Read the note
- Linux
- A free, open-source operating system family that runs most servers and network devices. Read the note
- LLDP
- Link Layer Discovery Protocol: lets devices learn about directly connected neighbours (vendor-neutral version of CDP). Read the note
- Load balancer
- A device or service that spreads traffic across several servers. Read the note
- Log
- A record of events produced by a system, application or device. Read the note
- LPWAN
- Low-power wide-area network, such as LoRaWAN, for battery IoT devices that send small amounts of data far. Read the note
M
- MAC address
- The hardware address of a network interface, written as six pairs of hexadecimal digits. Read the note
- MAC address table
- The table a switch uses to remember which MAC address is on which port. Read the note
- Malware
- Malicious software, including viruses, worms, trojans, spyware and ransomware. Read the note
- Man-in-the-middle
- An attack where someone secretly sits between two parties to read or change their traffic (also called on-path). Read the note
- MFA
- Multi-factor authentication: proving identity with two or more different factors, such as a password and a phone. Read the note
- Microsegmentation
- Dividing a network into very small zones so each workload only talks to what it needs. Read the note
- MITRE ATT&CK
- A public knowledge base of attacker tactics and techniques, used to plan detection and defence. Read the note
- MPLS
- Multiprotocol Label Switching: forwards packets using labels, widely used in provider WANs and VPNs. Read the note
- MQTT
- A lightweight publish/subscribe messaging protocol popular in IoT. Read the note
- MTU
- Maximum transmission unit: the largest packet a link can carry without splitting it (1500 bytes on standard Ethernet). Read the note
N
- NAC
- Network access control: checks devices and users before letting them onto the network. Read the note
- NAT
- Network Address Translation: changes private addresses to public ones so many devices can share an internet connection. Read the note
- NETCONF
- A protocol for configuring network devices using structured data (often with YANG models). Read the note
- Network segmentation
- Splitting a network into separate zones to limit the spread of attacks and problems. Read the note
- NFV
- Network functions virtualisation: running network functions like firewalls and routers as software. Read the note
- NGFW
- Next-generation firewall: a firewall that also identifies applications and users and can block threats. Read the note
- Nmap
- A free tool for discovering hosts and open ports on networks you are allowed to test. Read the note
- NTP
- Network Time Protocol: keeps device clocks in sync, which is vital for logs and certificates. Read the note
O
- OAuth
- A standard that lets an app access your data on another service without seeing your password. Read the note
- OSI model
- A seven-layer model that describes how network communication works, used as a troubleshooting checklist. Read the note
- OSINT
- Open-source intelligence: information gathered from public sources. Read the note
- OSPF
- Open Shortest Path First: a widely used link-state routing protocol inside organisations. Read the note
- OT
- Operational technology: systems that control physical processes in factories, utilities and buildings. Read the note
- OWASP Top 10
- A list of the most critical web application security risks, published by the OWASP community. Read the note
P
- PaaS
- Platform as a service: a cloud platform for running your applications without managing servers. Read the note
- Packet
- A unit of data at Layer 3, with source and destination IP addresses. Read the note
- Packet capture
- Recording network traffic for analysis, for example with Wireshark. Read the note
- PAM
- Privileged access management: protecting and monitoring admin accounts. Read the note
- Passkey
- A passwordless sign-in method based on public-key cryptography that resists phishing. Read the note
- Password manager
- An app that creates and stores strong, unique passwords for every site. Read the note
- Password spraying
- Trying a few common passwords against many accounts to avoid lockouts. Read the note
- PAT
- Port Address Translation (NAT overload): many inside devices share one public IP using different port numbers. Read the note
- Patch
- An update that fixes bugs or security vulnerabilities. Read the note
- Penetration testing
- An authorised, simulated attack to find and prove security weaknesses. Read the note
- Phishing
- Fake emails, messages or websites that trick people into giving away information or running malware. Read the note
- Ping
- A simple command that tests whether a device can be reached, using ICMP echo messages. Read the note
- PKI
- Public key infrastructure: the system of certificates, CAs and keys that makes secure websites and signatures work. Read the note
- PoE
- Power over Ethernet: sending power and data on the same cable to phones, cameras and access points. Read the note
- Port (network)
- A number (0–65535) that identifies a service on a device, such as 443 for HTTPS. Read the note
- Port security
- A switch feature that limits which or how many MAC addresses can use a port. Read the note
- Post-quantum cryptography
- New encryption methods designed to resist attacks by future quantum computers. Read the note
- PowerShell
- Microsoft’s command shell and scripting language for Windows administration. Read the note
- Private cloud
- Cloud-style infrastructure used by one organisation only. Read the note
- Private IP address
- An address from the reserved ranges 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, used inside networks. Read the note
- Protocol
- An agreed set of rules for how devices communicate. Read the note
- Proxy server
- A server that makes requests on behalf of clients, often to filter or cache web traffic. Read the note
- Public cloud
- Cloud services shared by many customers and run by a provider such as AWS, Azure or Google Cloud. Read the note
- Public key
- The shareable half of a key pair, used to encrypt data for its owner or check their signatures. Read the note
Q
- QoS
- Quality of service: giving important traffic, such as voice, priority on busy links. Read the note
- Quantum computing
- A new type of computing that could one day break today’s public-key encryption. Read the note
R
- RADIUS
- A protocol for central authentication, used for Wi-Fi, VPN and 802.1X sign-in. Read the note
- Ransomware
- Malware that encrypts or steals data and demands payment. Read the note
- RBAC
- Role-based access control: permissions are given to roles, and users get the roles for their job. Read the note
- Reconnaissance
- The information-gathering stage before an attack or penetration test. Read the note
- Redundancy
- Having spare components or paths so a single failure does not stop the service. Read the note
- REST API
- A common style of web API that uses HTTP methods such as GET and POST. Read the note
- Risk
- The chance that a threat will exploit a weakness, multiplied by the harm it would cause. Read the note
- Rootkit
- Malware that hides deep in a system to keep control and avoid detection. Read the note
- Router
- A device that connects different networks and forwards packets between them using IP addresses. Read the note
- Route summarisation
- Combining several networks into one shorter route to keep routing tables small. Read the note
- Routing table
- The list of networks a router knows and where to send traffic for each. Read the note
S
- SaaS
- Software as a service: ready-to-use applications delivered over the internet, such as Microsoft 365. Read the note
- Salt
- Random data added to a password before hashing so identical passwords get different hashes. Read the note
- SASE
- Secure access service edge: combining SD-WAN and cloud-delivered security into one service. Read the note
- SCADA
- Supervisory control and data acquisition: systems that monitor and control industrial processes. Read the note
- SDN
- Software-defined networking: separating the control of the network from the devices that forward traffic. Read the note
- SD-WAN
- Software-defined WAN: centrally managed wide-area networking that chooses the best path for each application. Read the note
- Security policy
- A written set of rules for how an organisation protects its information and systems. Read the note
- Server
- A computer that provides services, such as files, email or websites, to other devices. Read the note
- Serverless
- Running code in the cloud without managing servers; you pay per execution. Read the note
- SIEM
- Security information and event management: collects and correlates logs to detect threats. Read the note
- SMTP
- Simple Mail Transfer Protocol: used to send email between mail servers. Read the note
- SNMP
- Simple Network Management Protocol: used to monitor and manage network devices. Read the note
- SOAR
- Security orchestration, automation and response: tools that automate routine security tasks. Read the note
- SOC
- Security operations centre: the team that monitors, detects and responds to security threats. Read the note
- Social engineering
- Manipulating people into giving away information or access. Read the note
- Spanning Tree Protocol (STP)
- A switch protocol that prevents loops by blocking redundant paths. Read the note
- Spoofing
- Faking an identity, such as an email address, IP address or caller ID. Read the note
- Spyware
- Malware that secretly watches what a user does and sends the information to an attacker. Read the note
- SQL injection
- An attack that sneaks database commands into an input field to read or change data. Read the note
- SSH
- Secure Shell: an encrypted way to log in to and manage devices remotely. Read the note
- SSID
- The name of a Wi-Fi network. Read the note
- SSO
- Single sign-on: one login gives access to many applications. Read the note
- Static route
- A route typed in by hand rather than learned from a routing protocol. Read the note
- Subnet
- A smaller network created by dividing a larger IP network. Read the note
- Subnet mask
- The number that shows which part of an IP address is the network and which part is the host, such as 255.255.255.0. Read the note
- Supply chain attack
- Attacking a target through a trusted supplier, product or software update. Read the note
- Switch
- A device that connects devices within a network and forwards frames using MAC addresses. Read the note
- Syslog
- A standard way for devices to send log messages to a central server. Read the note
T
- TACACS+
- A Cisco-developed protocol for central authentication and command authorisation on network devices. Read the note
- TCP
- Transmission Control Protocol: reliable, connection-based delivery used by the web, email and file transfers. Read the note
- Terraform
- An infrastructure-as-code tool that builds cloud and network resources from configuration files. Read the note
- Threat
- Anything that could cause harm to a system, such as an attacker, malware or a flood. Read the note
- Threat actor
- A person or group behind an attack, such as cyber criminals, nation states or insiders. Read the note
- Threat hunting
- Proactively searching for hidden attackers instead of waiting for alerts. Read the note
- Threat modelling
- Thinking through how a system could be attacked so you can design defences early. Read the note
- TLS
- Transport Layer Security: encrypts traffic between apps and servers, including HTTPS. Read the note
- Topology
- The layout of how devices in a network are connected, such as star or mesh. Read the note
- Traceroute
- A command that shows each router on the path to a destination. Read the note
- Trojan
- Malware disguised as a useful program. Read the note
- Trunk
- A switch link that carries traffic for many VLANs. Read the note
- Two-factor authentication (2FA)
- Signing in with two different factors, such as a password and a code from an app. Read the note
U
- UDP
- User Datagram Protocol: fast, connectionless delivery used for DNS, voice and video. Read the note
- UTP cable
- Unshielded twisted pair copper cable, such as Cat5e and Cat6, used for Ethernet. Read the note
V
- Virtualisation
- Running several virtual computers or networks on one physical system. Read the note
- Virtual machine (VM)
- A software computer that runs its own operating system on shared physical hardware. Read the note
- Virus
- Malware that attaches to files or programs and spreads when they are run. Read the note
- VLAN
- Virtual LAN: a separate network created on a switch to keep groups of devices apart. Read the note
- VLSM
- Variable-length subnet masking: using different subnet sizes to fit each network’s needs. Read the note
- VoIP
- Voice over IP: making phone calls over a data network. Read the note
- VPN
- Virtual private network: an encrypted tunnel across an untrusted network such as the internet. Read the note
- VRF
- Virtual routing and forwarding: separate routing tables on one router to keep networks isolated. Read the note
- VRRP
- Virtual Router Redundancy Protocol: the open-standard way to share a backup default gateway. Read the note
- Vulnerability
- A weakness in software, hardware or a process that an attacker could exploit. Read the note
- Vulnerability scan
- An automated check for known weaknesses and missing patches. Read the note
W
- WAF
- Web application firewall: protects websites from attacks such as SQL injection and cross-site scripting. Read the note
- WAN
- Wide area network: a network that connects sites across cities or countries. Read the note
- Whaling
- Phishing aimed at senior executives. Read the note
- Wi-Fi
- Wireless local networking based on the IEEE 802.11 standards. Read the note
- Wi-Fi 7
- The newest Wi-Fi generation (802.11be), with wider channels and multi-link operation for higher speeds. Read the note
- Wildcard mask
- The inverse of a subnet mask, used in Cisco ACLs and OSPF to match address ranges. Read the note
- Wireshark
- A free tool for capturing and analysing network traffic. Read the note
- Worm
- Malware that spreads by itself across networks without user action. Read the note
- WPA3
- The latest Wi-Fi security standard, with stronger protection against password guessing. Read the note
X
- XDR
- Extended detection and response: combines signals from endpoints, network, email and cloud to detect attacks. Read the note
- XSS
- Cross-site scripting: injecting malicious script into web pages viewed by other users. Read the note
Y
- YANG
- A data modelling language that describes network device configuration and state for automation. Read the note
Z
- Zero-day
- A vulnerability that attackers use before the maker has released a fix. Read the note
- Zero Trust
- A security approach of “never trust, always verify”: every request is checked, wherever it comes from. Read the note
- Zigbee
- A low-power wireless mesh protocol used by smart-home devices. Read the note
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