multi-user dungeon

Meanings

1. A text-based online game in which players enter instructions on a command line to jointly engage in role-playing.
2. An early graphical massively multiplayer online game.

Etymology

From the title of the genre-defining 1978 video game Multi-User Dungeon, which was itself named to suggest a "multi-user" game that was otherwise similar to Dungeon, an unauthorized DEC-10 port of Zork. The title was not intended to imply a dungeon setting or any association with Dungeons & Dragons.