Two rays are opposite rays in geometry if they have a common initial point and form a straight line. Essentially, these rays point in opposite directions. The common initial point is also called the end point of a ray.
The opposite arms of a straight, 180-degree angle are an example of opposite rays.
A ray is a set of infinite points. It has length but no width. It stretches indefinitely in one direction only. Two opposite rays stretch indefinitely in both directions. All points on these two rays are collinear points.
A ray is a subset of a line. It always lies in a plane. Two opposite rays are subsets of the line that they form.