A device or program that separates data or signals in accordance with specified criteria.

See <<compensator>>

Any transmission network used in electrical systems for the selective enhancement of a given class of input signals. Also known as electric filter; electric-wave filter.

A porous article or material for separating suspended particulate matter from liquids by passing the liquid through the pores in the filter and sieving out the solids.

A device employed to reject sound in a particular range of frequencies while passing sound in another range of frequencies. Also known as acoustic filter.

A family of subsets of a set S: it does not include the empty set, the intersection of any two members of the family is also a member, and any subset of S containing a member is also a member.

An optical element that partially absorbs incident electromagnetic radiation in the visible, ultraviolet, or infrared spectra, consisting of a pane of glass or other partially transparent material, or of films separated by narrow layers; the absorption may be either selective or nonselective with respect to wavelength. Also known as optical filter.

In general, a selective device that transmits a desired range of matter or energy while substantially attenuating all other ranges.