Definition:
elevation: the vertical plane of an interior or exterior; see also
cross-section
An elevation is divided vertically into storeys: it can be a one-storey elevation, a two-storey elevation, a three-storey elevation or a four-storey elevation. The components of a storey can vary, and the variations are sometimes a matter of chronology or geography, particularly the use of a fourth storey.
bottom storey: arcade, colonnade or blind arcade
upper storeys: gallery, blind arcade, triforium, clerestory
The definitions below are also found in the glossary on http://www.pitt.edu/~medart.
triforium at clerestory level