Half Line

in mathematics, the set of points on a line that lie on one side of some point of the line. The coordinates x of the points of a half line satisfy one, and only one, of the inequalities x > a and x < a, where a is a constant. The point x = a is called the boundary of the half line. If the boundary is included in the half line, the half line is said to be closed. A closed half line is also called a ray.