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.
part of a circle, extending to the center; circular sector
section
a fictional region of space designated for navigational or governance purposes.
a field of economic activity
A fixed, continuous section of the track, such that sectors do not overlap but all sectors make up the whole track.
A toothed gear whose face is the arc of a circle.
an area designated by boundaries within which a unit operates, and for which it is responsible
zone (designated area).
one of the subdivisions of a coastal frontier
an instrument consisting of two rulers of equal length joined by a hinge.
An area of a crag, consisting of various routes
fixed-sized unit (traditionally 512 bytes) of sequential data stored on a track of a digital medium (compare to block)