Filter, filtering or filters may refer to:

Science and technology

Computing

* Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component that performs some operation on a multimedia stream * Email filtering, the processing of email to organize it according to specified criteria * Content-control software also known as an Internet filter * Wordfilter, a script typically used on Internet forums or chat rooms * Berkeley Packet Filter, filter expression used in the qualification of network data * DSL filter, a low-pass filter installed between analog devices and a telephone line * Helicon Filter, a raster graphics editor * Filter (large eddy simulation), a mathematical operation intended to remove a range of small scales from the solution to the Navier-Stokes equations * Kalman filter, an approximating algorithm in optimal control applications and problems

Device

* Filter (chemistry), a device which separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass ** Filter (aquarium), critical components of both freshwater and marine aquaria ** Filter paper, a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solids from liquids or air ** Air filter, a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air ** Oil filter, a filter to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil ** Pneumatic filter, a device which removes contaminants from a compressed air stream ** Water filter, removes impurities from water by means of a fine physical barrier, a chemical process or a biological process ** Cigarette filter, a part of a cigarette intended to filter the smoke inhaled by a smoker ** Coffee filter, a utensil used to separate coffee grounds from liquid coffee ** Fuel filter, found in most internal combustion engines ** Filtration (wine) * Sieve or macroscopic filter, a device for separating wanted elements from unwanted material

Mathematics

* Filter (mathematics), a special subset of a partially ordered set. * Filter (set theory), a special family of subsets that forms an (order theoretic) filter with respect to set inclusion * Filters in topology, the use of collections of subsets to describe convergence. * Filtering problem (stochastic processes), a mathematical model for a number of filtering problems in signal processing and the like. * Filtration (mathematics), an indexed set of subobjects of a given algebraic structure S.

Optics

* Optical filter, selectively transmits light of different wavelengths ** Interference filter, reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest ** Dichroic filter, a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors ** Hydrogen-alpha filter, an optical filter that transmits a narrow bandwidth of light centred on the H-alpha wavelength ** Photographic filter, a camera accessory consisting of an optical filter that can be inserted in the optical path ** Infrared cut-off filter, designed to reflect or block mid-infrared wavelengths while passing visible light ** Chelsea filter, a dichromatic optical filter used for identifying coloured stones ** Astronomical filter, a telescope accessory used to enhance the details of celestial objects

Signal processing

* Filter (signal processing) ** Electronic filter, an electronic circuit which processes signals, for example to remove unwanted frequency components ** Digital filter, a system that performs mathematical operations to reduce or enhance certain aspects of a signal ** Analogue filter, a basic building block of signal processing much used in electronics ** Filters used in Digital image processing#Filtering, digital image processing

Arts and entertainment

* Filter (TV series), ''Filter'' (TV series), a show on the G4 channel * Filter (magazine), ''Filter'' (magazine), an off-beat indie music magazine * Filter Theatre, a British theatre company * The Filter, a digital content services company based in England * Filter (band), an American rock band * "Filter", a song from the album ''Bend (8stops7 album), Bend'' by 8stops7 * "Filter", a song from the album ''Map of the Soul: 7'' by BTS

Social media

* Filter (social media), an appearance-altering digital image effect for social media * Beauty filter, a social media effect specifically meant to increase physical attractiveness

Other uses

* Category (Kant), Category-based filtering of perception, according to (objectivist interpretations of) Kant ** Affective filter, an impediment to learning or acquisition caused by negative emotional ("affective") responses to one's environment * Lane splitting, a practice that cyclists use to pass slow or stopped congested traffic *The ability of a person to self-Censorship, censor themselves (their thoughts) whilst speaking