annulus

Definition from Wiktionary, a free dictionary

[edit] English

[edit] Noun

annulus (plural annuluses)

1. A ring- or donut-shaped area or structure.
2. In mathematics, the region between two concentric circles of different radius.
3. In astronomy, the ring of the sun not covered by the moon in an annular solar eclipse.
4. (mycology) The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.