A ring- or donut-shaped area or structure.
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.
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.
Any topological space homeomorphic to the region in a plane between two concentric circles of different radius.
Any convex body or surface.
A playing card made convex for use in cheating.
A small convex mirror used to cheat by observing other players' cards.
arranged such that for any two points in the set, a straight line between the two points is contained within the set.
Curved or bowed outward like the outside of a bowl, circle, or sphere.
having no internal angles greater than 180 degrees.
having an epigraph that is a convex set.