The term filter may refer to:

• A device to separate mixtures. See filter (chemistry), filter (water), filter (air).

• A device to remove or block certain wavelengths (colors) of light. See filter (optics), filter (photography), infrared filter

• A computer program to process a data stream. See filter (software) , filter (Unix), mail filter, printer filter , Internet filter, lameness filter.

• An electronic or mechanical device, or mathematical algorithm, for processing signals. See electronic filter, signal processing, audio filter.

• In mathematics, a certain kind of subset of a partially ordered set. See filter (mathematics)

See also

• Affective filter, a type of learning blockage.
• Filter coffee, a hot drink
• Filter feeder, an animal that strains food particles from water
• Filter (band), a 1990s industrial rock band
• Philter, a magical charm