Acronyms
Oct 18, 2026 · Reference
Goal
Know these without looking them up. Format: acronym (what it stands for, what it does).
Networking
| Acronym | Stands for | What it does |
|---|---|---|
| ACK | Acknowledge | TCP flag: "I received your data" |
| APIPA | Automatic Private IP Addressing | 169.254.x.x address Windows gives itself when DHCP fails |
| ARP | Address Resolution Protocol | IP > MAC lookup on the local network |
| CAM | Content Addressable Memory | A switch's MAC address table |
| CDN | Content Delivery Network | Servers around the world that serve website files fast |
| CIDR | Classless Inter-Domain Routing | /number notation for subnet size (/24 = 254 hosts) |
| DHCP | Dynamic Host Configuration Protocol | Hands out IPs automatically, UDP 67/68 |
| DHCPv6 | DHCP for IPv6 | IPv6 version of DHCP, abused by mitm6 |
| DNS | Domain Name System | Names > IPs, UDP 53 |
| DoS | Denial of Service | Knocking a device or service offline |
| DoH | DNS over HTTPS | Encrypted DNS hidden inside HTTPS |
| DORA | Discover, Offer, Request, Acknowledge | The 4 steps of DHCP |
| ECH | Encrypted Client Hello | Hides the site name (SNI) in TLS |
| FIN | Finish | TCP flag: close the connection politely |
| ICMP | Internet Control Message Protocol | Ping and network error messages |
| IP | Internet Protocol | Logical address, Layer 3, used by routers |
| IPv4 | Internet Protocol version 4 | 192.168.12.34 style, 32 bits |
| IPv6 | Internet Protocol version 6 | fe80::... style, 128 bits |
| ISP | Internet Service Provider | The company that provides your internet |
| LAN | Local Area Network | Your home or office network |
| MAC | Media Access Control | Hardware address, Layer 2, used by switches |
| MSS | Maximum Segment Size | Largest data chunk per TCP packet (1460) |
| NAT | Network Address Translation | Router swaps private IP > public IP |
| NIC | Network Interface Controller | Network card (Wi-Fi, Ethernet) |
| OSI | Open Systems Interconnection | The 7-layer network model |
| PPP | Point-to-Point Protocol | Layer 2 protocol for a direct link between two devices |
| OUI | Organizationally Unique Identifier | First 3 bytes of a MAC = manufacturer |
| pcap | Packet capture | Captured traffic file (.pcap, .pcapng) |
| PDU | Protocol Data Unit | One complete message at a given layer |
| PSH | Push | TCP flag: send this data to the app now |
| QUIC | Quick UDP Internet Connections | HTTPS over UDP 443, no TCP handshake |
| RST | Reset | TCP flag: "go away" / "nothing's here" |
| SACK | Selective Acknowledgment | Resend only the lost TCP packet |
| SNI | Server Name Indication | Site name sent in plain text in the TLS Client Hello |
| SYN | Synchronize | TCP flag: start a connection |
| TCP | Transmission Control Protocol | Reliable, handshake first, Layer 4 |
| TLS | Transport Layer Security | The encryption behind HTTPS |
| UDP | User Datagram Protocol | Fast, no handshake, Layer 4 |
| URG | Urgent | TCP flag: urgent data, rarely used |
| VLAN | Virtual LAN | Splits one switch into separate networks |
| WAN | Wide Area Network | The internet side of your router |
| WS | Window Scale | Lets the TCP window grow past 65,535 bytes |
Protocols and services (with ports)
| Acronym | Stands for | What it does |
|---|---|---|
| FTP | File Transfer Protocol | File transfers, port 21 |
| HTTP | Hypertext Transfer Protocol | Unencrypted web, port 80 |
| HTTPS | HTTP Secure | Encrypted web, port 443 |
| IMAP | Internet Message Access Protocol | Read email on the server, port 143 |
| LDAP | Lightweight Directory Access Protocol | Query Active Directory, port 389 |
| NetBIOS | Network Basic Input/Output System | Old Windows file sharing / naming, port 139 |
| NTP | Network Time Protocol | Clock sync, UDP 123 |
| POP3 | Post Office Protocol v3 | Download email, port 110 |
| RDP | Remote Desktop Protocol | Windows remote desktop, port 3389 |
| RPC | Remote Procedure Call | Windows services talking to each other, port 135 |
| SMB | Server Message Block | Windows file sharing, port 445 |
| SMTP | Simple Mail Transfer Protocol | Send email, port 25 |
| SNMP | Simple Network Management Protocol | Device monitoring, UDP 161 |
| SSH | Secure Shell | Encrypted remote terminal, port 22 |
| TFTP | Trivial File Transfer Protocol | File transfer with no login, UDP 69 |
| WinRM | Windows Remote Management | Remote PowerShell, ports 5985/5986 |
Hacking and attacks
| Acronym | Stands for | What it does |
|---|---|---|
| AD | Active Directory | Windows domain: users, computers, logins for a company |
| CTF | Capture The Flag | Hacking practice challenges |
| LLMNR | Link-Local Multicast Name Resolution | Windows' fallback name lookup, poisoned by Responder |
| MITM | Man-in-the-Middle | Attacker sits between two victims and sees their traffic |
| NBT-NS | NetBIOS Name Service | Older fallback name lookup, also poisoned by Responder |
| OSINT | Open Source Intelligence | Recon from public information |
| PrivEsc | Privilege Escalation | Going from a normal user to admin/root |
Systems and tools
| Acronym | Stands for | What it does |
|---|---|---|
| OS | Operating System | Windows, Linux, macOS |
| VM | Virtual Machine | A computer running inside software (Kali, lab targets) |
| WSL | Windows Subsystem for Linux | Runs Linux inside Windows |
Courses and certs
| Acronym | Stands for | What it is |
|---|---|---|
| TCM | TCM Security | The company behind PEH and PNPT |
| PEH | Practical Ethical Hacking | The course I am taking now |
| PJPT | Practical Junior Penetration Tester | Entry cert after PEH |
| PNPT | Practical Network Penetration Tester | The main cert I am working toward |
| HTB | Hack The Box | Hacking labs and HTB Academy courses |
| CPTS | Certified Penetration Testing Specialist | HTB's multi-day practical pentest exam |
| OSCP | Offensive Security Certified Professional | OffSec's 24-hour hands-on pentest exam (PEN-200 course) |
| CRTO | Certified Red Team Operator | Red team cert |
| BSCP | Burp Suite Certified Practitioner | Web app hacking cert from PortSwigger |
| Security+ | CompTIA Security+ | Entry-level security certification |
Security teams and platforms
| Acronym | Stands for | What it is |
|---|---|---|
| SOC | Security Operations Center | Team that watches alerts and responds to attacks |
| AppSec | Application Security | Team that secures a company's own software |
| PSIRT | Product Security Incident Response Team | Team that handles vulnerabilities found in a company's products |
| AWS | Amazon Web Services | Amazon's cloud platform |
| DC | Domain Controller | The server that runs AD (Active Directory) |
OSI (Open Systems Interconnection) model
Moved to its own note: OSI Model.