Ne znam je li kolega mislio na ovo, kada je u pitanju napisao "dio zgrade", ali evo sta kazu izvori:
http://en.wikipedia.org/wiki/Bay_(architecture)
A bay is a unit of form in architecture. This unit is defined as the zone between the outer edges of an engaged ('attached') column, pilaster, or post; or within a window frame, doorframe, or vertical 'bas relief' wall form.
A bay, on either the exterior (facade) or interior walls of a building, can be either the opening (void) in the wall, usually consisting of a window between the window frame or a doorway between doorframe; or the wall (solid) between an architectural element such as a buttress, or column.
A bay can refer to the number of vertical divisions of the exterior or interior surfaces of a building, as marked by these elements. For example in Georgian style, at Mulberry Fields, the building is described as a "5 bay by 2 bay facade," meaning a "5 windows by 2 windows" exterior.
A bay can also be the individual volumes (units) of space defined by the vertical piers (supports) and overhead vaults (between ribs), in a building using a vaulted structural system. For example, the Gothic architecture period's Chartres Cathedral has a nave (main interior space) that is "seven bays long."