Spandrel

n.	1.	(Arch.) The irregular triangular space between the curve of an arch and the inclosing right angle; or the space between the outer moldings of two contiguous arches and a horizontal line above them, or another arch above and inclosing them.
	2.	A narrow mat or passe partout for a picture.

Noun

1.

spandrel - an approximately triangular surface area between two adjacent arches and the horizontal plane above them Synonyms: spandril

spandril, surface