A circle is a plane figure, bounded by a single curve line called its circumference, every part of which is equally distant from a point within it, called the center.

A circle sector is any piece of the circle between two radial lines (shaded in both dark and clear grey).

A segment of a circle is the region between a chord of a circle and its associated arc (shaded in dark grey).

An annulus is the region lying between two concentric circles

Areas