### Theory:

Line
A line is obtained by extending the line segment infinitely in both directions. It has an infinite number of points. A line is labelled sort of a line segment with a bidirectional arrow over the label.

The above figure shows a line $$AB$$ and is represented as $$\overleftrightarrow {AB}$$ or $$\overleftrightarrow {BA}$$. Sometimes the line is denoted by a letter like $$m$$, as showed in the above line.
Example:
The $$100$$ metres track is to illustrate the concept of the line. A track may be a line that extends infinitely in both directions without having a fixed starting and ending point.
Ray
A ray is a part of a line. It starts at one point and extends infinitely in the opposite direction. The ray has an infinite number of points.
The starting point that's fixed at one end is termed as a vertex of a ray.

The above figure shows a ray $$AB$$ and is represented as $$\overrightarrow{AB}$$.

Important!
A ray name should start with a vertex and end in another direction.

The name of the above ray is $$\overrightarrow{AB}$$ not $$\overrightarrow{BA}$$.
Example:
We have a battery-operated torch on one end of the road and, light from the torch (called as line segment) is travelling in a straight line towards the other direction. Since we don't know the end of that light, we will say that this line segment from a fixed source is a ray.