What is a geometric term for a part of a line defined by two endpoints?

A segment is the correct term for a part of a line defined by two endpoints. In geometry, a segment specifically refers to the straight line that connects the two endpoints, including all points between them. This distinction is important because it emphasizes that the segment has a definite length, unlike a line, which extends infinitely in both directions, or a ray, which starts at one point and extends indefinitely in one direction. An arc, on the other hand, refers to a portion of a circle, which is quite different from the linear nature of a segment.