(Multi User Dimension, MultiUser Dimension, Multi-User Dungeon, Multi User Dungeon, MultiUser Dungeon, Multi-User Domain, Multi User Domain, MultiUser Domain) n. A game, such as GemStone III, which is played simultaneously with multiple players. Most MUDs are of relatively poor quality and are run by people in their spare time, though some MUDs, such as GemStone III, are of a high level of quality and are professionally created and maintained.

See also: GemStone III.