What is a Ray?

Hint: Ray is an example of line that covers all the distances from its starting point in a straight path in any direction. So, we can say that a ray is an example of a line or a segment of line. Since, a line does not have any direction but it has two points with start and end. But ray has one point and another always shows its direction.

Complete step-by-step solution:
Ray is an idealized model of light that covers a distance in a straight path. Therefore, in Mathematics, we will define it as an example or form of line that contains only one side starting or ending point and the other side will continue moving in the form of line. Since, we cannot define the starting or ending point for it but we can observe that it always travels in a straight line. We can check it by taking coordinates of any point lying in the line, which will give the distance from starting points to that point. So, we can say that it travels in a straight path.
Here is diagram of straight line that contains both starting and ending points that is $AB$ as:

As we saw the diagram of line; we will see the diagram of ray below as:

In this diagram, we clearly see that there is not any starting or ending point. But if take $A$ as a starting and will start moving it into the direction of $D$ . We can say that $AD$ is a ray in the direction towards $D$ will denote as $\overrightarrow{AD}$ , where $A$ is the starting point and $D$ is the direction of ray.
Similarly, we can take the a ray as $\overrightarrow{DA}$ , where $D$ is the starting point and $A$ is the direction.
So, we can take any point as a starting point and another point shows its direction towards that point with the help of an arrow above the notation.

Note: The most important notable thing in a ray is it always shows a direction or we can say that it moves or travels into a direction. So, when we represent its points with the help of an arrow above the notation that means the arrow denotes the direction towards that point. As we saw in the solution, $\overrightarrow{AD}$ denotes $A$ as a starting point and $D$represents its direction because the arrow denoted the direction towards $D$ .