The dividing line or location between two areas.

plural of boundary

Enclosed by a boundary or boundaries. / (in combination, by extension) Enclosed by a boundary or boundaries of a specified kind.

(of a compact topological space with boundary) Having had some but not all of its boundary removed.

plural of boundary umpire

plural of boundary rider

Alternative form of boundary rider

(Australia) A person employed to travel along the boundary of a station, to check and maintain the fencing.

An internal interface that separates neighbouring misoriented single crystals in a polycrystalline solid.

(Australian rules football) A match official who decides when the ball has over the boundary line (out of bounds), and whether it was on the full from a kick. (Under the rules as of 2007, a free kick results from on the full, or a throw-in otherwise.)