A MUD (Multi-User Dungeon or, sometimes, Multi-User Dimension) is a network-accessible, multi-participant, user-extensible virtual reality whose user interface is entirely textual. Participants (usually called players) have the appearance of being situated in an artificially-constructed place that also contains those other players who are connected at the same time. Players can communicate easily with each other in real time. This virtual gathering place has many of the social attributes of other places, and many of the usual social mechanisms operate there. Certain attributes of this virtual place, however, tend to have significant effects on social phenomena, leading to new mechanisms and modes of behavior not usually seen IRL (in real life)." —Pavel Curtis