Words made up from the initial letters of other words.
Abbreviations written as the initial letter or letters of words, and pronounced based on this abbreviation (e.g., NASA, National Aeronautics and Space Administration).
Special acronyms are used for chat rooms, and to a lesser extent, email. If you want the full experience of a chat room, you should study up on your web acronyms or at least keep this cheat sheet handy.
6, 7 A word formed from the initial letter or letters of each word in a set of words (e.g., NATO, radar).
Short form for a group of words. See Sol: chat-o-rama: Acronyms 'R' Us