## IGD: Line, Ray, Segment

A *line* is straight, flat, and extends infinitely in two directions. Through any two points, there is one and only one line that can be drawn. Two lines either intersect in one point, or they are *parallel* and never intersect. The term "straight line" is also used to refer to a line.

A *segment* is a finite portion of a line and is determined by its two endpoints. A segment consists of its two endpoints together with all the points on the line that are between the endpoints. The length of a segment is a measure of its size and is the same as the distance between its endpoints. The terms "line segment" and "straight line segment" are also used to refer to a segment.

A *ray* is a portion of a line and goes on infinitely in one direction. It is determined by one endpoint and any other point that shows which half of the line constitutes the ray. A ray consists of its endpoint and all points on that half of the line.