Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the "adsorbate" on the surface of the "adsorbent". This process differs from absorption, in which a fluid (the "absorbate") is dissolved by or permeates a liquid or solid (the "absorbent"), respectively. Adsorption is a "surface phenomenon", while absorption involves the whole volume of the material, although adsorption does often precede absorption. The term "sorption" encompasses both processes, while "desorption" is the reverse of it.