a gallery or arcade in the wall above the arches of the nave, choir, or transept of a church
Origin of triforiumMedieval Latin from Classical Latin tri-, tri- + foris, door
nounpl. tri·fo·ri·a, Architecture
An arcaded gallery above the side-aisle arches and below the clerestory of a church.
Origin of triforiumMedieval Latin a gallery in Canterbury Cathedral (later taken to mean “with three openings”)