a station established at a distance from the main body of an army to protect it from surprise attack: We keep only a small garrison of men at our desert outposts.
2.
the body of troops stationed there; detachment or perimeter guard.
3.
an outlying settlement, installation, position, etc.
1757, "military position detached from the main body of troops," from out + post (2). Originally in George Washington's letters. Commercial sense of "trading settlement near a frontier" is from 1802. Phrase outpost of Empire (1912) echoes Kipling.