A geometric ray has one endpoint and extends from the endpoint to infinity in one direction on a line. Rays are written with a right-facing arrow over two capital letters. The first letter represents the endpoint, and the second letter represents another point on the ray.
When two rays share a common endpoint, they form an angle. The endpoint is called the vertex, and the two rays are called arms. If the two rays overlap, the angle measures 0 degrees and appears as one ray. If the two rays point in exactly opposite directions, the angle measures 180 degrees and appears as a straight line. Any other combination of the two rays results in an angle between 0 degrees and 360 degrees.