MUD

A screenshot of a MUD

A multi-user dungeon (MUD, /mʌd/), also known as a multi-user dimension or multi-user domain, is a multiplayer real-time virtual world, usually text-based or storyboarded. MUDs combine elements of role-playing games, hack and slash, player versus player, interactive fiction, and online chat. Players can read or view descriptions of rooms, objects, other players, and non-player characters, and perform actions in the virtual world that are typically also described. Players typically interact with each other and the world by typing commands that resemble a natural language, as well as using a character typically called an avatar.