A window is an opening in the wall or building that function to admit light or air. In a masonry wall, a window is a brick, block or stone opening into which a window unit can be placed. Openings may incorporate window ledges and arches.
A bay is a unit of form in architecture. This unit is defined as the zone between the outer edges of an attached column, pilaster, or post; or within a window frame, doorframe, or vertical ‘bas relief’ wall form. A bay on the walls of a building can be the opening in the wall consisting of a window between the window frame