Line, ray, Line segment

If we join two points, we get line segment.

We write line segment AB as (AB)  or (BA)  

Here, points A and B are the end points of the line segment.

Line

A line extends in definitely in both directions.

A line as no end point.

We write line  AB  as (AB) 

Ray

Ray is a line with one end-point.

Here AB is a ray.

It can extend from point B, but point A is fixed.

We write it as (AB) 

Similarly,

(PQ) is a ray