**Line Segment:**

A line segment is a part of a line that has two endpoints. It is a straight path between two points. The length of a line segment can be measured using a ruler or any other measuring tool.

**Explanation:**

A line is a straight path that extends infinitely in both directions. It has no endpoints. For example, if you draw a line on a piece of paper, you can extend it indefinitely in both directions.

A ray is a straight path that extends infinitely in one direction. It has one endpoint and goes on forever in the other direction. For example, if you draw a ray on a piece of paper, you can extend it infinitely in one direction but not in the other.

A point is a location in space. It has no length, width, or height. It is represented by a dot. For example, if you mark a dot on a piece of paper, it represents a point.

A line segment, on the other hand, is a part of a line that has two endpoints. It is a finite length and can be measured. For example, if you draw a line segment on a piece of paper, it has a definite length between the two endpoints.

In the context of the given question, the set of points that is a part of a line with two endpoints is a line segment. This is because a line segment is the only option that fits the description of having two endpoints and being a part of a line. A line does not have endpoints, a ray extends infinitely in one direction, and a point is a single location without any length. Only a line segment has the characteristics of being a part of a line and having two endpoints.

Therefore, the correct answer is option B - A line segment.