Consider the line:

Point B is between points A and C, and A, B and C are collinear.

Segment AC consists of points A and C and all points in between A and C. Points A and C are called the endpoints of the segment AC.

Segment AC, denoted as

Ray AC consist of points A and C and all points P such that C is between A and P. Point A is the endpoint of the ray. When denoting a ray, its endpoint is named first.

Ray AC, denoted as

Two rays with a common endpoint which extend indefinitely in opposing directions are called opposite rays. All the points on both rays are collinear with each other.