Absorption has a number of meanings:

• In physics, absorption is a process in which particles of some sort encounter another material and are taken up by or even disappear in it. Specifically, it can refer to:

• Volume absorption of particles of gas or liquid in liquid or solid material is studied in physical chemistry.
• In optics absorption refers to the absorption of photons by a material.
• In acoustics absorption refers to the absorption of sound waves by a material.

Absorption should not be confused with adsorption, the formation of a liquid or gas film on a solid surface.