Filter

Filter, filtering or filters may refer to:

Science and technology[edit]

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 (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

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 (mathematics), a special subset of a partially ordered set.
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.

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