What's the 3D causticity?

"caustics" means that when light passes through a transparent object, due to the unevenness of the surface of the object, the refraction of light does not occur in parallel, and diffuse refraction occurs, resulting in photon dispersion on the projection surface.

caustics is an indirect lighting effect that is easy to identify. The principle of caustics is actually very simple: indirect illumination light (i.e. photons) passes through a light source once (or many times)? Specular? Surface reflection and refraction, then projected on a Diffuse surface, and finally captured by the camera in the form of Diffuse? Record? . The Specular surface in this process is called? Caustic projection object? , Diffuse surface is called? Caustic receiving object? .