a part of an army or military force detached from the main body to bring up and guard the rear from surprise attack, esp. in a retreat.
rear•guardPronunciation: (rēr'gärd"), [key]
of or pertaining to a rear guard.
designed to oppose or prevent in a defensive way: a rearguard strategy. Also,rear'-guard".
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.