Filtration is a separation process in which a solid-liquid mixture called the feed (or the suspension) is forced through a porous medium on which the solids are deposited or in which they are entrapped. The porous medium which allows the liquid to go through while retaining the solids is called the filter. The retained solid is called "the residue" or "the cake". The clarified liquid is called "the effluent" or the "filtrate".