All of the rays from a directional light source have a common direction, and no point of origin. It is as if the light source was infinitely far away from the surface that it is illuminating.

Sunlight is an example of an infinite light source.

The direction from a surface to a light source is important for computing the light reflected from the surface. With a directional light source this direction is a constant for every surface.

A directional light source can be colored.