Absorb - This term refers to the process where one substance is taken into another through permeation or dissolution. In absorption, the substance fully penetrates into the absorbing material. For example, a sponge absorbs water.
Adsorb - This term is used to describe a process where atoms, ions, or molecules from a substance (such as a gas or liquid) adhere to the surface of an adsorbent material. Adsorption is a surface-based process.