Filter

Look up Filter, filter, filtering, or filters in Wiktionary, the free dictionary.

Filter may refer to:

Chemistry, engineering and materials

Filter (aquarium), critical components of both freshwater and marine aquaria
Filter (chemistry), a device (usually a membrane or layer) that is designed to physically block certain objects or substances while letting others through
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. Filters cleanse water to various extents for irrigation, drinking water, aquariums, and pools

In optics and photography, a device to remove, or to enhance, certain ranges of wavelengths (colors) of light. See:

Filter (optics), including types:
- Interference filter
- Dichroic filter
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
H-alpha filter, a specific red visible spectral line created by hydrogen with a wavelength of 6562.8 Å
Chelsea filter
Astronomical filter, a telescope accessory used to enhance the details of celestial objects.

In turbulence modeling, a procedure to dampen or remove the highest frequencies of the flow:

Filter (large eddy simulation), in the context of large eddy simulation (LES) is a mathematical operation intended to remove a range of small scales from the solution to the Navier-Stokes equations

In signal processing, especially electronics, an algorithm or device for removing part(s) of a signal:

Filter (signal processing), especially,
- 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.

In computing:

Filter (higher-order function), a higher-order function that processes a data structure (typically a list) in some order to produce a new data structure containing exactly those elements of the original data structure for which a given predicate returns the boolean value true
A program to process a data stream:
- Filter (software), a computer program to process a data stream
- Filter (Unix), a program that gets most of its data from its standard input (the main input stream) and writes its main results to its standard output (the main output stream)
- Filter (video)
- Email filter
- Internet filter
- Wordfilter, a script typically used on Internet forums or chat rooms that automatically scans users' posts or comments as they are submitted and automatically changes or censors particular words or phrases
BPF filter expression used in the qualification of network data
DSL filter, a low-pass filter installed between analog devices and a telephone line

Category-based filtering of perception — according to (objectivist interpretations of), Kant

In mathematics, a certain kind of subset of a partially ordered set. See
- Filter (mathematics), a special subset of a partially ordered set
- Filtering problem (stochastic processes), a mathematical model for a number of filtering problems in signal processing and the like
In psychology, a type of learning blockage. See
- Affective filter, an impediment to learning or acquisition caused by negative emotional ("affective") responses to one's environment. It is a hypothesis of second language acquisition theory, and a field of interest in educational psychology
In transportation. See
- Lane splitting, a practice that cyclists use to pass slow or stopped congested traffic

Filter (band), an American rock band
Filter (TV series), a show on the G4 channel
Filter (magazine), an off-beat indie music magazine
Helicon Filter, a raster graphics editor
Filter (theatre company)
The Filter, a digital content services company based in England
Kalman filter, an approximating algorithm in optimal control applications and problems