Desorption is a phenomenon and process opposite of adsorption, absorption or more general sorption . Desorption process occurs in a system being in the state of adsorption equilibrium between bulk phase (fluid, i.e. gas or liquid solution) and adsorbing surface (solid, or boundary separating 2 fluids) and when the concentration (or pressure) of adsorbed/absorbed/sorbed substance in the bulk phase is lowered. The result is the decrease of the amount of adsorbed/absorbed/sorbed substance.