The elements that comprise the church are:
Nave arcades – A series of arches supported by columns or piers.
Tribunes – An upper story over the aisle which opens onto the nave or choir. It corresponds in length and width to the dimensions of the aisle below it.
Triforium – A narrow passage in the thickness of the wall with arches opening onto the nave. It may occur at the level of the clerestory windows, or it may be located as a separate level below the clerestory. It may itself have an outer wall of glass rather than stone.
Clerestory – An upper story of a building with windows above adjacent roofs.
Hemicycle – The group of columns, arranged in a semicircular formation, that divide the east end of a choir from the ambulatory.
Example: In the image above, Section A (Laon) shows the arcade, tribune, triforium, and clerestory levels.
All definitions are from the Glossary of Medieval Art and Architecture.