These words denote a line that marks the outermost part of an area, or a division between areas. Boundary is used chiefly of territory, and suggests a definite demarcation, such as a line or mark that can be precisely located on a map. Bounds are less definite, and may be used figuratively of behaviour: His impudence exceeds all bounds . In military usage out of bounds serves to notify military personnel not to enter the building or area so stigmatized. This use is extended to any area forbidden to certain persons: The girl’s recreation area in the school is out of bounds to boys. The colloquial expression out of bounds , derived from its use in various sports, is commonly used with the meaning of unfair, improper or indecent: Holding hands was out of bounds , and as for kissing ?that was unthinkable.

Whereas boundary points to an outermost limit, border emphasizes the division between two areas: the border between the U.S.S.R. and Finland.

• He crossed the border into Belgium; By international agreement the boundary of each nation fronting a body of water extends exactly three miles from the coastline.

Border often suggests a territorial feature, such as a river or mountain range, and hence is not as precise as boundary . Boundaries may be changed by treaties, i.e. on paper; borders may change by the changing course of a river or by military action.

Limit is the most general term of this group, and can be applied to any outermost extent, range, demarcation, etc. as here considered the term is usually plural: to pass beyond the city limits . Frontier may refer to the part of a nation’s territory lying along the border of another country; it thus describes the border region of a country from an interior perspective. Frontier also means the part of a settled region lying along the border of an unsettled region; the frontier towns of the American Wild West. Frontier is often used in extended senses; beyond the frontier of knowledge; at the frontier of space exploration.

Confines , like bounds , defines the extent of an area without reference to what lies beyond, but confines is less consistently restricted to the description of geographical limits : He was not permitted to pass beyond the confines of his room. Confines , like bounds , is commonly used figuratively: His genius soared beyond the narrow confines of his education; beyond all bounds of decency or common sense.