Filter

Filtration is a physical process that separates solid matter and fluid from a mixture. Filter, filtering, filters or filtration may also refer to:

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


 * Filter (social media), an appearance-altering digital image effect for social media

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

Arts and entertainment

 * Filter (TV series), a show on the G4 channel
 * Filter (magazine), an 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 by 8stops7
 * "Filter", a song from the album Map of the Soul: 7 by BTS

Other uses

 * Filtering (housing), the process of housing units becoming more affordable with age
 * 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-censor themselves (their thoughts) whilst speaking