filters locus

a. device that selectively blocks some wavelengths of light or other signals while allowing others to pass; b. colored glass, gel, or other medium placed in front of or behind a lens; c. criteria or mechanism for selection; d. a permeable screen, membrane, or other mechanism used to separate materials by size; e. to filter: the act of using a filter.

Getty AAT: Any porous material, such as paper or sand, through which a gas or liquid is passed to separate out matter in suspension. (AAT 300015133)