RC - Rules Cyclopedia.
Retro-Clone - A replica of an out-of-print game, usually based on a previous version of D&D, but not limited to that. Many retro-clones take advantage of the OGL.
RQ - RuneQuest
Rules Cyclopedia - A compilation of the D&D Basic BECMI ruleset in hardcover format.
S&W - Swords & Wizardy.
Sandbox - A style of campaign play where there is no pre-scripted plot the players are guided to, rather the actions of the players help determine the direction the campaign takes.
SRD - System Reference Document, a compilation of OGC released onder the OGL by WotC.
Swords & Wizardry - An 0E D&D retro-clone.
WotC - Wizards of the Coast, the current owners and publishers of Dungeons & Dragons.
That's all I've found so far. If anyone knows of any more that should be on the list, just let me know!
50 minutes ago