The Collaborative International Dictionary of English v.0.48:

Outpost \Out"post`\, n. (Mil.)
   (a) A post or station without the limits of a camp, or at a
       distance from the main body of an army, for observation
       of the enemy.
   (b) The troops placed at such a station.
       [1913 Webster]

WordNet (r) 3.0 (2006):

outpost
    n 1: a station in a remote or sparsely populated location [syn:
         outstation, outpost]
    2: a settlement on the frontier of civilization [syn: frontier
       settlement, outpost]
    3: a military post stationed at a distance from the main body of
       troops