MUD In online gaming, a MUD (Multi-User Dungeon), pronounced /mʌd/, is a multi-user real-time virtual world described entirely in text. It combines elements of role-playing games, hack and slash, interactive fiction, and online chat. Players can read descriptions of rooms, objects, other players, non-player characters, and actions performed in the virtual world. Players interact with each other and the world by typing commands that resemble a natural language.