In acoustics, diffusion is the scattering of sound waves to reflect them in different directions. Or breaking the soundwaves into smaller pieces.
Diffusion is commonly used to reduce specular reflections and echo. Also to direct sound energy to specific areas.

The purpose of a diffuser is to break up sound waves and disperse them in various directions.
There are two main types of diffuser, the barrel diffuser and the quadratic diffuser.
Adding sound diffusion to your acoustic room treatment can improve the speech and instrument intelligibility and improve the overall listening environment within the room