MUDs (multi-user dungeons or dimensions)(note) have most of the
following characteristics: several people can play at once; the game
is partioned into virtual spaces ("rooms") such that people and
objects in one room cannot directly interact with people and objects
in another room; all interaction takes place in text, not pictures or
sounds; communications are handled with TCP sockets; most of the code
is written and maintained by university students and is available in
the public domain; combinations of objects, rooms and exits allow
simple puzzles, while some MUDs with their own programming languages
allow for much more complicated puzzles and toys; even MUDs created
for serious purposes retain some of the original Adventure or
role-playing game atmosphere; and since identities aren't constrained
by reality, the characters on muds include close facsimiles of the
people who play them, furry animals, science fiction heros, and all
ranges of cute, profane, obnoxious, witty, or just plain weird.(note)