POSTERN
, or Sally-port, in Fortification, a small gate, usually made in the angle of the flank of a bastion, or in that of the curtain, or near the orillon, defcending into the ditch; by which the garrison can march in and out, unperceived by the enemy, either to relieve the works, or to make private sallies, &c.—It means also any private or back door.