A midpoint is the halfway point of a line segment. Only line segments can have a midpoint. A line cannot have a halfway point because a line goes on indefinitely in both directions.
A line segment on a coordinate plane is defined by two endpoints. A coordinate plane is a two-dimensional graph that has a vertical y-axis and a horizontal x-axis. Application of the midpoint theorem facilitates discovery of the coordinates of the midpoint. The theorem states that the coordinates of the midpoint of a line segment are the average of the coordinates of its endpoints. Therefore, the x-coordinate of the midpoint is the average of the x-coordinates of the two endpoints, and the y-coordinate is the average of the y-coordinates of the two endpoints.