A MU* is a text-based online role-playing game. Players create characters and then roleplay 'scenes' between them, in virtual rooms which represent the local world. This roleplay consists of a series of 'poses' — descriptions of what the character says or does, and sometimes of things in the environment — generally performed in turn by each player in the scene. It's sort of like doing improv in text, although many if not most games also have 'stats' which suggest what a given character's abilities are, and use dice to determine how well they work in a given situation, or against another PC ('player character') or NPC ('non-player character'). I like to think of it as a form of collaborative storytelling.