What is an eccentric circle?

Eccentric circles are circles that do not share the same center although the centers of each circle are all contained within at least one of the circles. The opposite of eccentric circles are concentric circles.

In order for circles to be eccentric, the inner circles must be off-center of the outermost circle. The word "eccentric" itself means "deviating from the accepted or customary practice" or "irregular." The word was first utilized in the English language as an astronomy term which referred to the perceived irregular motions of celestial bodies. It then expanded into a geometry term with the above meaning.