When two rays share an endpoint, an angle is formed. Below, the rays and create angle
When referring to a specific angle, the notation is often used to name the angle. Additionally, is used to note the size or measure of an angle, which can be interpreted as the amount of turn in the rotation between the rays. It is often measured in degrees, but can also be measured in radians. An angle of shows no rotation, while an angle of shows a complete rotation.
Sometimes, the space outside an angle — rather than inside — is of interest. In figure above, measures the interior angle formed by the rays, whereas measures the exterior angle.