Programs that accept input data and modify it in some way before passing it on. For example, the pr command is a filter.

A device that passes or blocks certain frequencies or groups of frequencies.

in electronics, a circuit that only passes certain signals. For blood flow measurement, a low pass filter is often used to strip out high frequency noise, leaving only the biological components of interest.

The analogue or digital means of removal of unwanted noise from the data, based on its frequency content. Frequency regions beyond the spectral content of the response are attenuated whilst the frequency band of interest is not. The upper and lower boundaries of the "pass band" are usually separate high-pass (rejecting low frequencies) and low pass (rejecting high frequencies) filters.

Devices that remove unwanted noise or interference in electrical circuits or contaminants in hydraulic oil.

A passive RF component which passes or rejects a signal solely on the basis of its frequency. There are four main categories of filters: low pass, high pass, bandpass, and band reject.

GTMS assemblies used to eliminate unwanted frequencies from an electronic signal.

A device placed over a light source or a sensor to select or reject specific frequencies of light.

Small, fast programs in a firewall that examine packets as they arrive at the firewall, and route or reject the packets based on user-definable rules.