Diffusion

A physical process taking place within a fluid, by means of which a given property of it, or a quantity of material particles contained within it, is propagated. It occurs both at the molecular level and through turbulent motions, at different scales, as happens in the atmosphere (turbulent diffusion). The term is also used in reference to the process resulting from the interaction of electromagnetic radiation with the molecules of the material medium it passes through (for example, sunlight in the atmosphere), which is more commonly expressed as scattering.