bai·ley 
(bālē)
(bālē)n. pl. bai·leys
1. A wall or palisade surrounding the structures protected by a medieval fort or castle, especially the outer wall of a castle.
2. The space enclosed by this wall.
[Middle English bailli, from Old French baille, probably from Latin bacula, pl. of baculum, log, stick; see BACILLUS.]