triforium
Tri*fo"ri*um, n. Etym: [LL., fr. L. tri- (see Tri-) + foris, pl. fores, a door.] (Arch.) Defn: The gallery or open space between the vaulting and the roof of the aisles of a church, often forming a rich arcade in the interior of the church, above the nave arches and below the clearstory windows.