[acronym, Multi-User Dungeon; alt. Multi-User Dimension]
1. n. A class of virtual reality experiments accessible via the Internet. These are real-time chat forums with structure; they have multiple 'locations' like an adventure game, and may include combat, traps, puzzles, magic, a simple economic system, and the capability for characters to build more structure onto the database that represents the existing world.
2. vi. To play a MUD (see hack-and-slay). The acronym MUD is often lowercased and/or verbed; thus, one may speak of 'going mudding', etc.
Historically, MUDs (and their more recent progeny with names of MUform) derive from an AI experiment by Richard Bartle and Roy Trubshaw on the University of Essex's DEC-10 in the early 1980s; descendants of that game still exist today (see BartleMUD). The title 'MUD' is still trademarked to the commercial MUD run by Bartle on British Telecom (the motto: "You haven't *lived* 'til you've *died* on MUD!"); however, this did not stop students on the European academic networks from copying and improving on the MUD concept, from which sprung several new MUDs (VAXMUD, AberMUD, LPMUD). Many of these had associated bulletin-board systems for social interaction. Because USENET feeds have been spotty and difficult to get in the U.K. and the British JANET network doesn't support FTP or remote login via telnet, the MUDs became major foci of hackish social interaction there.
AberMUD and other variants crossed the Atlantic around 1988 and quickly gained popularity in the U.S.; they became nuclei for large hacker communities with only loose ties to traditional hackerdom (some observers see parallels with the growth of USENET in the early 1980s). The second wave of MUDs (TinyMUD and variants) tended to emphasize social interaction, puzzles, and cooperative world-building as opposed to combat and competition. In 1991, over 50% of MUD sites are of a third major variety, LPMUD, which synthesizes the combat/puzzle aspects of AberMUD and older systems with the extensibility of TinyMud. The trend toward greater programmability and flexibility will doubtless continue.
The state of the art in MUD design is still moving very rapidly, with new simulation designs appearing (seemingly) every month. There is now (early 1991) a move afoot to deprecate the term MUD itself, as newer designs exhibit an exploding variety of names corresponding to the different simulation styles being explored.