The region in a plane between two concentric circles of different radii.
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 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.
Also, the plane in which this great circle lies.
A great circle drawn on a terrestrial globe, used for illustrating and solving astronomical problems.
The great circle on the celestial sphere that is the mean apparent path of the sun as viewed from the earth.
Relating to an eclipse or the ecliptic.