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Filter may refer to:


Chemistry, engineering and materials

In chemistry, engineering, or household usage, a device to separate mixtures. See:

Optics and photography

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

Signal processing

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


In computing:



Proper name

See also



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Wikipedia has articles on:


See also Filter





(noun) From Mediaeval Latin filtrum, from West Germanic *filtiz.




filter (plural filters)

  1. A device which separates a suspended, dissolved, or particulate matter from a fluid, solution, or other substance; any device that separates one substance from another.
  2. Electronics or software that separates unwanted signals (for example noise) from wanted signals or that attenuates selected frequencies.
  3. Any item, mechanism, device or procedure that acts to separate or isolate.
    • He runs an email filter to catch the junk mail.
  4. A proper subset of a poset A, which subset includes an element less than both of every pair of its members, and includes every element more than each of its members.
    The collection of cofinite subsets ofis a filter under inclusion: it includes the intersection of every pair of its members, and includes every superset of every cofinite set.

Derived terms


The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Help:How to check translations.


to filter

Third person singular

Simple past

Past participle

Present participle

to filter (third-person singular simple present filters, present participle filtering, simple past and past participle filtered)

  1. (transitive) To sort, sift, or isolate.
    • This strainer should filter out the large particles.
  2. (transitive) To diffuse; to cause to be less concentrated or focused.
    • The leaves of the trees filtered the light.
  3. (intransitive) To pass through a filter or to act as though passing through a filter.
    • The water filtered through the rock and soil.
  4. (intransitive) To move slowly or gradually; to come or go a few at a time.
    • The crowd filtered into the theater.
  5. (intransitive) To ride a motorcycle between lanes on a road
    • I can skip past all the traffic on my bike by filtering.


  • (to sort, sift, or isolate) to filter out (something)


The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Help:How to check translations.

Related terms




filter n. (singular definite filtret or filteret, plural indefinite filtre)

  1. filter




filter m. and n. (plural filters, diminutive filtertje, diminutive plural filtertjes)

  1. filter



filter n.

Inflection for filter Singular Plural
neuter Indefinite Definite Indefinite Definite
Base form filter filtret filter filtren
Possessive form filters filtrets filters filtrens
  1. A filter.

Simple English

A filter is a device used to remove unwanted parts from something. For example, removing solid particles from a liquid. Filter can also mean the act of filtering: it can be used as a verb. The different branches of science and technology often mean a particular kind of device when filter is mentioned.


In chemistry

The simplest filter is the kind called filter paper. Liquids can pass through the paper. Solid particles are stopped.

More advanced filters are possible. Two that are often used to make water more pure are activated carbon and zeolites.

In electrical science

The most usual thing meant by filter in electrical science is a wave filter. This is a filter which will let through some frequencies and stops all others. For instance, a filter can be used in a radio to select the station the listener wants to hear. The frequency of that station is passed, but all others are rejected.

There are many other uses, including use in telephones and audio.

There are digital filters which can be used to filter things besides frequencies. A common use is to improve the quality of pictures. For instance, there are filters which can make the edges of objects look more clear.

In optics and photography

Optical filters act on light. They change it certain ways. This can be used for photographic filters.

In mechanics

Filters can be made from mechanical components. They will do very similar things to electric filters. Most especially, mechanical filters can be wave filters. That is, they can block some frequencies and pass others. Because of this, electric filters are sometimes made by first making a mechanical filter. The electric wave is turned into a mechanical movement, then passed through the filter, then turned back in to an electric wave. This kind of filter is often made from quartz crystals.

A device which changes electrical signals into mechanical signals is called a transducer. A device which changes mechanical signals into electrical signals is also a transducer, but one of a different kind.

In information technology

An internet filter removes certain kinds of information. For example, certain words can be blocked.


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