The story
By analogy with annulus, which is the region enclosed by two concentric circles.
Etymology from Wiktionary, CC BY-SA 4.0.
square annulus
Today it means: the region enclosed by two concentric squares with parallel sides Full definition →
Today it means: the region enclosed by two concentric squares with parallel sides Full definition →
By analogy with annulus, which is the region enclosed by two concentric circles.
Etymology from Wiktionary, CC BY-SA 4.0.