- For the shipping term, see Absorption (shipping)
In general, absorption is the movement of a substance into another substance. Different disciplines use absorption in different ways.
In chemistry, absorption is when a solute in one phase crosses a phase boundary into another phase. It is generally called absorption when the goal is to move a solute into another phase; when the goal is to move the solute out of a phase, it is called adsorption.
In physics, absorption is the process by which radiant energy is retained by a substance. A further process always results from absorption, that is, the irreversible conversion of the absorbed radiation into some other form of energy within and according to the nature of the absorbing medium. The absorbing medium itself may emit radiation, but only after an energy conversion has occurred.