What is "central angle"

n. (context geometry English) An angle positioned with its vertex at the center of a circle.

A central angle is an angle whose apex (vertex) is the center O of a circle and whose legs (sides) are radii intersecting the circle in two distinct points A and B. The central angle is subtended by an arc between those two points, and the arc length is the central angle (measured in radians) times the radius. The central angle is also known as the arc's angular distance.

The size of a central angle Θ is 0°<Θ<360° оr 0<Θ<2π (radians). When defining or drawing a central angle, in addition to specifying the points A and B, one must specify whether the angle being defined is the convex angle (<180°) or the reflex angle (>180°). Equivalently, one must specify whether the movement from point A to point B is clockwise or counterclockwise.