God rays
Visible shafts of light streaming through clouds, windows or foliage as light scatters off particles in the air — almost pure mood lighting.
Meteorology calls the phenomenon crepuscular rays, and it happens when light bounces off dust and haze. Real-time rendering fakes it. A cheap and popular method is a post-process radial blur outward from the sun's screen position, using the depth buffer to mask whatever occludes it — the approach the Crysis era made common. Costlier variants ray-march through a field of volumetric fog.
The effect does nothing mechanically; it is pure atmosphere, which is exactly why screenshots love it. Through the late-2000s HDR-and-bloom era it was overused to the edge of parody — for a while every doorway seemed to admit divine light.