Xeen is the world in which Might and Magic IV and Might and Magic V take place. Like the other games in the original universe continuity, XEEN starts as an artificial nacelle environment like VARN, CRON, and the Isles of Terra. Its original name, given by the Ancients, was X.E.E.N., which stands for Xylonite Experimental Expansion Nacelle.
Interestingly enough, XEEN is an artificial world in two parts, one on each side of the flat "planet", and each game is set on one half of the same world. If both games are installed on the same hard drive, the player has the ability to traverse the barriers between the worlds at will (via teleporters), which will unlock dungeons, if accessible, in the two games, as well as a third ending in which the Cube of Power and Sceptre of Temporal Distortion are used in a Unification ceremony that transforms XEEN into the round fully-fledged planet Xeen.