A radian is a unit of measurement for angles. One radian is defined as the angle that is subtended by an arc of a circle with a length equal to the radius of the circle. This means that if you drew a radius from the center of a circle to the circumference, and then drew an arc that was the same length as that radius, the angle at the center of the circle between the two radii would be one radian. Radians are a standard unit of measurement for angles, and they are used in many mathematical and sc