In mathematics, a line segment is a part of a line that is bounded by two end points. See also interval (mathematics).
When the end points both lie on a curve such as a circle, a line segment is called a chord (of that curve). When they are both vertices of a polygon, it is an edge (of that polygon) if they are adjacent vertices, and otherwise a diagonal (of it).
The midpoint of a line segment is its 'middle' point: the unique point at an equal distance from the two end points.