What is a ray in math?

In math, a ray is part of a line that has an endpoint at its starting point and extends in a certain direction into infinity. Drawing a ray involves placing a line with one endpoint and an arrow point on the other end. To name a ray, the convention is to use the letter at the starting point followed by a letter near the arrow point.

One can use capital letters to name a ray, and over the two letters is drawn a ray symbol. An alternate convention used to name a ray is to use one lower case letter.

Two rays that diverge from a common starting point are called an angle. Another name for this starting point is the vertex of the angle.