What is "framing square"

Usage examples of "framing square".

It seemed a part of the forest about it, save for the unusual straightness of its limbs, and within moments they were close enough to see that it was a series of giant girders, covered with rust and framing square portions of the open sky.

Within the largest framing square was a circle, within the circle a smaller square, its angles aligned to the compass points.

Red carpet from wall to wall, red drapes framing square rain-blurred windows, green and red chintz covered armchairs, a cocktail bar lined with red leather covered stools in one corner, a Formica-topped table to seat eight near the door: in the corner opposite the bar, a curtained-off alcove.