A ray is a one-dimensional shape comprising half an infinite line, with a point as a boundary on one end. Because it is one dimensional with an uncountably infinite number of points and a single pointlike boundary, it is topologically equivalent to the half-open line segment.

It can be visualised as the nonnegative part of a number line covering all finite numbers, or alternately as the subset of the Euclidean line with nonnegative coordinates.