Editing Filter (section)

==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
* [[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#Filtering|digital image processing]]