The scattering of light in many directions as the result of reflection from an uneven surface or passage though a translucent material: Jane wanted to have a thin curtain in front of her window to produce diffusion in the living room so she could read without the glaring sunlight from outside blinding her.

The exchange of fluid parcels between regions in the atmosphere in the apparently random motions of a scale too small to be treated by the equations of motion: Mr. Fox explained the expression atmospheric diffusion by using an example of air pollutants in the air.