You searched for: “annulus
annulus (AN yuh luhs)
1. A ringlike figure, part, structure, or marking; such as, a growth ring on the scale of a fish.
2. A ring or group of thick-walled cells around the sporangia of many ferns that functions in spore release.

The ringlike remains of a broken partial veil, found around the stipes of certain mushrooms.

3. In mathematics, the figure bounded by and containing the area between two concentric circles.