(gen) The taking in, incorporation or reception of gases, liquids, light or heat. (phys/chem.) Penetration of one substance into the inner structure of another (cf. adsorption, in which one substance is attracted and held on the surface of another). Occurs between a gas or vapor and a liquid. (pharm.) The process of movement of a drug from the site of application into the extracellular compartment of the body.