Tech people love abbreviations. Most of them don't even know how to resolve the abbreviations. Relax and smile knowingly - you found the most important explanations here:

Abbreviation Long term
2FA → 2-Factor Authentication
A11y Numeronym for accessibility (A + 11 characters + y)
ACID Atomicity, Consistency, Isolation, Durability → ACID
API Application Programming Interface
ATAG Authoring Tool Accessibility Guidelines → ATAG
BIENE Barrierefreies Internet eröffnet neue Einsichten“ (German accessibility award)
BITV Barrierefreie Informationstechnik-Verordnung (German directive similar to → WCAG)
BSD Berkeley Software Distribution
CAS Central Authentication Service → CAS
CC → Creative Commons
CLI Command Line Interface
CMIS Content Management Interoperability Services (open standard)
CMS Content Management System
CRM Customer Relationship Management
CSS Cascading Style Sheets
DAM Digital Asset Management → Media Asset Management
ELTS Extended Long Term Support
EoL End of Life
ERP Enterprise Resource Planning → ERP
FLOSS/FOSS Free(/Libre) and Open Source Software
FTP File Transfer Protocol
GmbH German: Gesellschaft mit beschränkter Haftung - a legal form similar to Inc.
GNU → GNUProject
GPL GNU General Public License
GUI Graphical → User Interface
GWT Google Web Toolkit
HTML 5 Hypertext Markup Language, version 5
i18n Numeronym for internationalization (i + 18 characters + n)
IoT Internet of Things
JSP Java Server Pages
JSR Java Specification Request
LDAP Lightweight Directory Access Protocol → LDAP
Less Less CSS → Stylesheet Language
LGPL GNU Lesser General Public License
LTS Long Term Support
MIT Massachusetts Institute of Technology (here referring to a license type)
MPL Mozilla Public License
MVC → Model View Controller
MVP → Minimum Viable Product
OOP Object-Oriented Programming
OSS Open Source Software
PHP Hypertext Preprocessor – programming language
PHP-FIG PHP Framework Interop Group → PHP-FIG
RDF Resource Description Framework → Semantic Web
REST Representational State Transfer → REST
ROI Return on Investment
SAML → Security Assertion Markup Language
SEO Search Engine Optimization
SFTP Secure File Transfer Protocol (FTP)
SOAP Simple Object Access Protocol
SQL Structured Query Language – database language
SSH Secure Shell - cryptographic network protocol
TFA → 2-Factor Authentication
UI → User Interface
W3C World Wide Web Consortium → W3C
WAI Web Accessibility Initiative → WAI
WCAG Web Content Asseccibility Guidelines
WYSIWYG What you see is what you get → WYSIWYG
XML Extensible Markup Language
XSL Extensible Stylesheet Language
XSLT XSL Transformation (for XML documents)
XSS → Cross-Site Scripting

Find explanations for most of these terms in our glossary.