AAnas Mahmood·October 15, 2026·3 min read·security fundamentals
// TL;DR
A grouped, corrected reference of the acronyms you’ll run into constantly in security and computing — from network and protocol terms to attack types, hardware, and the classics. I’ve sorted them by category so they’re easy to scan, fixed the expansions that are commonly mistyped, and separated out the “backronyms” (fun folklore that isn’t actually what the term stands for) so you don’t quote a myth in a report.
Attacks & offensive security
Abbr.
Expansion
CSRF
Cross-Site Request Forgery
XSS
Cross-Site Scripting
SQLi
SQL Injection
DoS
Denial of Service
DDoS
Distributed Denial of Service
RCE
Remote Code Execution
LFI
Local File Inclusion
RFI
Remote File Inclusion
SE
Social Engineering
RAT
Remote Access Trojan / Remote Administration Tool
FUD
Fully Undetectable
NOP
No Operation
Defensive & detection
Abbr.
Expansion
IDS
Intrusion Detection System
HIDS
Host-based Intrusion Detection System
NIDS
Network-based Intrusion Detection System
CAPTCHA
Completely Automated Public Turing test to tell Computers and Humans Apart
VPN
Virtual Private Network
WEP
Wired Equivalent Privacy
WPA
Wi-Fi Protected Access
WPS
Wi-Fi Protected Setup
Networking & protocols
Abbr.
Expansion
AP
Access Point
API
Application Programming Interface
CDN
Content Delivery Network
CDMA
Code Division Multiple Access
DNS
Domain Name System
FTP
File Transfer Protocol
HTTP
HyperText Transfer Protocol
HTTPS
HyperText Transfer Protocol Secure
IP
Internet Protocol (as in IP address)
IRC
Internet Relay Chat
ISN
Initial Sequence Number
ISP
Internet Service Provider
LAN
Local Area Network
MAC
Media Access Control (physical address)
MAN
Metropolitan Area Network
POP
Post Office Protocol
SSH
Secure Shell
SSL
Secure Sockets Layer
URL
Uniform Resource Locator
WAN
Wide Area Network
WiFi
Wireless Fidelity (marketing term; not a true acronym)
WLAN
Wireless Local Area Network
WWW
World Wide Web
4G
Fourth Generation (mobile network)
Web & application
Abbr.
Expansion
HTML
HyperText Markup Language
CSS
Cascading Style Sheets
PHP
PHP: Hypertext Preprocessor (recursive)
SQL
Structured Query Language
DBMS
Database Management System
CLI
Command-Line Interface
GUI
Graphical User Interface
UI
User Interface
WML
Wireless Markup Language
VBA
Visual Basic for Applications
Operating systems & software
Abbr.
Expansion
OS
Operating System
DOS
Disk Operating System
MS-DOS
Microsoft Disk Operating System
BIOS
Basic Input/Output System
BSOD
Blue Screen of Death
APK
Android Package Kit
EXE
Executable (file format)
IDM
Internet Download Manager
BASIC
Beginners’ All-purpose Symbolic Instruction Code
GW-BASIC
Gee-Whiz BASIC (Microsoft dialect)
CLS
Clear Screen (command)
DIR
Directory (command)
DEL
Delete (command)
REM
Remark (comment)
JMP
Jump (assembly instruction)
Hardware & storage
Abbr.
Expansion
CPU
Central Processing Unit
PC
Personal Computer
ATA
Advanced Technology Attachment
SATA
Serial Advanced Technology Attachment
DIMM
Dual In-line Memory Module
SIMM
Single In-line Memory Module
DSP
Digital Signal Processor
MODEM
Modulator-Demodulator
SIM
Subscriber Identity Module
USB
Universal Serial Bus
ATM
Automated Teller Machine
General computing & data
Abbr.
Expansion
PDF
Portable Document Format
JPEG
Joint Photographic Experts Group
OCR
Optical Character Recognition
IM
Instant Messaging
DTP
Desktop Publishing
EDP
Electronic Data Processing
EDI
Electronic Data Interchange
EC
Electronic Commerce
MIS
Management Information System
IVRS
Interactive Voice Response System
PID
Process Identifier (also Product ID, by context)
ENIAC
Electronic Numerical Integrator and Computer
EDSAC
Electronic Delay Storage Automatic Calculator
EDVAC
Electronic Discrete Variable Automatic Computer
MANIAC
Mathematical Analyzer, Numerical Integrator and Computer
Backronyms & myths
These circulate widely but aren’t the real origins of the terms. They’re fun — just don’t put them in a report as fact.
Term
Popular “expansion”
Reality
VIRUS
“Vital Information Resource Under Seize”
A backronym. Virus is simply the Latin word for poison, applied to self-replicating code.
WINDOWS
“Wide Interactive Network Development for Office Work Solution”
Pure myth. Microsoft Windows is named for its on-screen windows, not an acronym.
LINUX
“Linus’ UNIX”
A loose nickname, not an official acronym — named after creator Linus Torvalds.
ORACLE
“Oak Ridge Automatic Computer and Logical Engine”
That machine existed, but the database company’s name is unrelated folklore here.
UNIX
“Uniplexed Information and Computing Service”
Originally UNICS, a pun on the earlier MULTICS — later smoothed to “Unix.” Not the expansions usually listed.
Know one I missed? Drop it in the comments. Happy hacking!
Anas Mahmood
Web & API penetration tester and bug bounty hunter. I write up the bugs I find and the methods that found them.
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