There are several definitions of a ray.
When viewed as a vector, a ray is a vector from a point to a point .
In geometry, a ray is usually taken as a half-infinite line (also known as a half-line) with one of the two points
and taken to be at infinity.
More things to try:
Weisstein, Eric W. "Ray." From MathWorld--A
Wolfram Web Resource. https://mathworld.wolfram.com/Ray.html