Definitions
1.nounA ring- or donut-shaped area or structure.
2.nounThe region in a plane between two concentric circles of different radii.
3.nounAny topological space homeomorphic to the region in a plane between two concentric circles of different radius.
4.nounThe ring of the sun not covered by the moon in an annular solar eclipse.
5.nounStructure in a fern that consists of differentially thick-walled cells on a sporangium that bend and distort as a result of drying.
6.nounThe membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
7.noun(oil and gas production) The space contained between the centre well bore and any external tubing. Sometimes used for separated gas flow.