Any topological space homeomorphic to the region in a plane between two concentric circles of different radius.
The ring of the sun not covered by the moon in an annular solar eclipse.
Structure in a fern that consists of differentially thick-walled cells on a sporangium that bend and distort as a result of drying.
A ring- or donut-shaped area or structure.
The region in a plane between two concentric circles of different radii.
The membranous remnants of a partial veil which leaves a ring on the stem of a mushroom.
The space contained between the centre well bore and any external tubing. Sometimes used for separated gas flow.
A topological space which is a product of two circles.
The thickening of a membrane closing a wood-cell pit (as of gymnosperm tracheids) having the secondary cell wall arched over the pit cavity.
A rounded ridge of bone or muscle, especially one on the occipital bone.
{{lb|en|topology|in combination|n-torus|4-torus|etc.}} The product of the specified number of circles.
A large convex molding, typically semicircular in cross section, which commonly projects at the base of a column and above the plinth.
The end of the peduncle or flower stalk to which the floral parts (or in the Asteraceae, the florets of a flower head) are attached.
A ring-shaped object, especially a large ring-shaped chamber used in physical research.