In a MUD or MMO, zone and area are terms used to refer to one of the parts of the shared virtual environment.
They should not be confused with levels (where a player proceeds through a series of stages in a linear or semi-linear manner).
The environments of MUDs and MMOs may be seamlessly sewn together, in which case it may be difficult or impossible for the player to know the precise boundaries of a particular area, or they may be connected by connector zones (such as the classic sight-line blocking z-shaped corridor) or portals.
In some games it is possible to note changes in area through different flora and fauna, altered livery of guards, or special skills.
Many MUDs are hybrids, containing sections which are seamlessly stitched together alongside other areas which are only accessible via portals, etc.