Concentric

Two geometric figures are concentric if their centers coincide. The region between two concentric circles is an annulus.

The following table summarizes some concentric central circles.

Kimberling	center	circles
	incenter	Adams' circle, Conway circle, hexyl circle, incircle
	triangle centroid	inner Napoleon circle, outer Napoleon circle
	circumcenter	circumcircle, second Brocard circle, second Droz-Farny circle, Stammler circle
	orthocenter	anticomplementary circle, polar circle, first Droz-Farny circle
	nine-point center	nine-point circle, Steiner circle
	Spieker center	excircles radical circle, Spieker circle
	Brocard midpoint	Gallatly circle, half-Moses circle, Moses circle
	midpoint of the Brocard diameter	Brocard circle, first Lemoine circle