This is an Image Effect used to create Crepuscular Rays.
This goes a little further than the intrinsic Unity3D version, you are able to use your own texture for the light source, you can place it anywhere in a 2D or 3D scene...
Soft Alpha UI Mask
Dec 20, 2016 2:18 AM
Shaders that allow you to have soft alpha blending on your UI elements rather than the built in hard alpha mask