Spandrel
A spandrel is a roughly triangular space, usually found in pairs, between the top of an arch and a rectangular frame, between the tops of two adjacent arches, or one of the four spaces between a circle within a square. They are frequently filled with decorative elements. In a building with more than one floor, the term spandrel is also used to indicate the space between the top of the window in one story and the windowsill on the story above.