Directional light
Light that falls in one direction at uniform strength everywhere, standing in for a distant sun.
Every ray is parallel and the light has no position, only a direction — the source is treated as infinitely far away, so intensity never attenuates. It is the cheapest light type: a single direction vector drives the whole scene, and one flat shadow map (usually split into cascades to hold up at range) covers everything in view.
Almost always used for sun- or moonlight in outdoor scenes. Because every surface is lit from the same angle, the directional light is also the easiest case for shading models — Blinn-Phong can skip computing a reflection vector entirely. A scene rarely has more than one.