Why Is It Called A MUCK?

MUCK is an acronym, but the words for which it supposedly stands is debatable.
This is probably because MUCKs are actually derivations of MUDs, which were the original multiplayer text adventures created in 1979 by a student at Essex University named Roy Trubshaw. At the time, the internet was still in its infancy, but Roy programmed his text adventure to utilize the internet to allow players from all over the world to log in and participate. The original adventures were programmed around the popular Dungeons and Dragonsroleplaying games, with players exploring dungeons or similar medieval settings. The game was thereby named a 'MUD' or Multi-User Dungeon.

MUSHes and MUCKs were introduced a few years later. They were variants on the original MUD codebase that had been reprogrammed in various ways. Their names were taken from obvious variants on 'MUD', and imbued with meaning later. MUCK is usually said to refer to 'Multi-User Chat Kingdom', which is appopriate given that MUCKs are considerably more chat/socially focused than MUDs. In fact, MUCK's original codebase dispensed with the combat system entirely, and it has only been in recent derivations of MUCKs (such as GlowMUCK) that MUD-style gaming capabilities have been programmed back in.

Today there are many variants of the original MUDs in existence. Many combat-themed MUDs still exist, as well as MUCKs, MUSHes, MOOs, MUXes, MUQs, etc. Each variant has its pros and cons, but they all reamain largely true to the text-adventure style and spirit.