What does "annulus" mean?

Annulus: (Geom.) (a) A space contained between the circumferences of two circles, one within the other. (b) The solid formed by a circle revolving around a line which is the plane of the circle but does not cut it.

Additional senses

  1. 2.(Zoöl.) Ring-shaped structures or markings, found in, or upon, various animals.

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