A line segment is a part of a line that is bounded by two distinct endpoints, and contains every point on the line between its endpoints
In the figure above, the line segment would be called segment AB because it links the two points A and B. The bar over the two letters indicates it is a line segment, rather than a line, which goes on forever in both directions.
A ray is the part of the line which consists of the given point and the set of all points on one side of the end point.
In the figure, the ray would be called AB because starts at point A and passes through B on it’s way to infinity. The single arrow over the second letter indicates it is a ray, and the arrow direction indicates that A is the point where the ray starts.
Opposite rays are two rays that both start from a common point and go off in exactly opposite directions. Because of this the two rays form a single straight line through the common endpoint T.
When the two rays are opposite, the points B, T, and R are collinear.
