The term filter may refer to:

• Filter (chemistry) — a device to separate mixtures, e.g. filter (water), filter (air) , etc..
• Filter (signal processing) — a device or algorithm for signal processing (e.g. audio filter).
• Filter (optics) and filter (photography) (e.g. infrared filter, ND filter , UV filter ) — a device that blocks certain wavelength ranges of light.
• Filter (Unix) — in Unix, any program with standard I/O streams.
• Filter (software) — any software that processes a data stream (e.g. mail filter, printer filter , Internet filter, lameness filter).
• Filter (mathematics) — a certain kind of subset of a partially ordered set.
• An affective filter is a learning blockage.
• A filter feeder is an animal that strains food particles from water.

Filter was also the name of a 1990s industrial rock band; see Filter (band).

See also

• List of filter terms
• Philter.