Other forms: spandrels
In architecture, a spandrel is the triangle-shaped space between two arches, or between an arch and the rectangle that frames it. Often, a spandrel is formed by a wall, a ceiling, and the curve of an arch.
In some structures, the spandrel is a space that's filled with decoration — Paris's Arc de Triomphe, for example, has spandrels at the top corners of its three arches, each carved with ornamental figures. Buildings constructed during the Gothic period commonly have elaborately decorated spandrels. The word comes from the Anglo-French spaundre, which is thought to be a shortened version of espandre, "expand or spread" in Old French.