Filter (chemistry), a device (usually a membrane or layer) that is designed to physically block certain objects or substances while letting others through
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. Filters cleanse water to various extents for irrigation, drinking water, aquariums, and swimming pools
Interference filter - An interference filter or dichroic filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorp...
Dichroic filter - A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors.
Photographic filter, a camera accessory consisting of an optical filter that can be inserted in the optical path
Filter (higher-order function), a higher-order function that processes a data structure (typically a list) in some order to produce a new data structure containing exactly those elements of the original data structure for which a given predicate returns the boolean value true
Filter (Unix), a program that gets most of its data from its standard input (the main input stream) and writes its main results to its standard output (the main output stream)
Filter (video) - A video filter is a software component that is used to decode audio and video.
Email filter - Email filtering is the processing of email to organize it according to specified criteria.
Internet filter - Content-control software, content filtering software, secure web gateways, censorware, web filtering software, content-censoring software, and content-blocking s...
Wordfilter, a script typically used on Internet forums or chat rooms that automatically scans users' posts or comments as they are submitted and automatically changes or censors particular words or phrases
BPF filter expression used in the qualification of network data
DSL filter, a low-pass filter installed between analog devices and a telephone line
Affective filter, an impediment to learning or acquisition caused by negative emotional ("affective") responses to one's environment. It is a hypothesis of second language acquisition theory, and a field of interest in educational psychology
Lane splitting, a practice that cyclists use to pass slow or stopped congested traffic