The term diffusion is used in various fields, including the Science of matter and telecommunications.
Science of matter
The action of spreading out to reach a uniform state; the result of this action. In the case of light, the sending out in all directions of light striking the surface of a body. This is also called diffuse reflection, which differs from ordinary diffusion in that the direction of the diffused radiation is not related to that of the incident radiation.
In the case of light, we refer to diffusion when the light is sent in various directions after meeting an obstacle. © DR