Absorption

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 in the inner part (called "bulk") of a gas, liquid, or solid material.

This is a different process from adsorption. Molecules undergoing absorption are going deep into the volume of the material, instead in the case of adsorption molecules stop at the surface of the material. A more general term is sorption, which covers absorption, adsorption, and ion exchange.

Other meanings of "absorption" are:

• Biology: entry of substances through the skin or other boundaries such as the intestine or cell membrane.
• Pharmacology: release of drugs into the blood.
• Physics: receiving of electromagnetic radiation by a material.