Last modified on April 1, 2009, at 22:05

A ray is a portion of a line which starts at a given point and continues endlessly in one direction. Intuitively, it can be thought of as "half" a line because it extends infinitely in only one direction rather than two, opposite directions as lines do. Of course, quantitatively, "half a line" is somewhat meaningless since a line is infinite and half of infinity is still infinity.