Absorption is a condition in which something takes in another substance. It is a physical or chemical phenomenon or process, in which atoms, molecules, or ions enter a 'bulk phase' – gas, liquid, or solid material.
This is a different process from adsorption. Molecules undergoing absorption are taken up by the volume, not by the surface (as in the case for adsorption). A more general term is sorption, which covers absorption, adsorption, and ion exchange.
- Chemistry: absorption of a gas or liquid in a liquid or solid medium.
- Biology: entry of substances through the skin or other boundaries such as the intestine or cell membrane.
- Pharmacology: absorption of drugs into the blood.
- Physics: absorption of electromagnetic radiation by a material.
- Such as diffusion, for example.