Filter

Filtration is a physical process that separates solid matter and fluid from a mixture.

Filter, filtering, filters or filtration may also refer to:

Science and technology

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

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

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.

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

Biofilter, a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants
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