MUD is a acronym for multi-user dungeon (or dimension), a role-playing computer game that runs on a bulletin board system or Internet server. Many people may connect simultaneously. Once connected, players control a character. They see textual descriptions of rooms, objects, other characters, and computer-controlled creatures or NPCs (non-player characters) in a virtual world. Players may interact with each other and the surroundings by typing commands that resemble plain English.
Most MUDs implement a fantasy world populated by elves, goblins, and other mythical beings. Players pretend to be knights, sorcerers, and the like. The goal of the game is to slay monsters and complete quests. Some MUDs have a science fiction setting. Most MUDs are run as hobby and are free to players.
The popularity of MUDs escalated in the USA during the 1980s, when (relatively speaking) cheap, at-home PCs with 300 to 2400 baud modems enabled role players to log into multi-line BBSes. In Europe, MUD development and use centered around academic networks around the same time. The MUD scene is still very much alive on the Internet, accessed via telnet. Specialized telnet clients exist that give a more pleasant user experience.
Some common MUD servers are SMAUG and DikuMUD.
Once computer power increased and Internet connectivity became ubiquitous, the graphical MMORGs (massively multiplayer online role-playing games) developed. Unlike earlier MUDs, most MMORGs are commercial ventures. Examples of MMORGs include:
The original MUDs drew their inspiration from paper-and-pencil based games such as Dungeons and Dragons (hence their name), but over time variants have diversified into other models while retaining the textual format. For example, some variants are called MUCKs, MUSHs, LPMUDs, and MOOs.
A MUSH is often said to mean multi-player shared hallucination. MUSHes descend from the program TinyMUD. MUSHes date back to the early 1990s. They are more direcly concerned with role-playing than MUDs, dispensing with the scoring system and most rules.
Other variants emphasize building by providing players with a powerful programming language (as in MOOs) to make their own objects and rooms, or function as elaborate chat systems with no fantasy trappings.