The word boundary has a variety of meanings.

• In general, the term boundary is something that encloses a region space, a territory, and/or an area. Something enclosed by a boundary, is "bounded" (by the boundary). See also border.
• For boundary in the sport of cricket, see: boundary (cricket).
• For the boundary of a set in a topology, see: boundary (topology).
• For the boundary of a topological manifold, see: manifold,
• As a psychological term, boundary can mean a mental separation which we keep between ourselves and others. Sometimes this can be referred to as personal space. Addicts use boundaries to keep themselves sober.