- 1 a device containing paper, sand, chemicals, etc. that a liquid or gas is passed through in order to remove any materials that are not wanted an air/oil filter a coffee/water filter He smokes cigarettes without filters.
- 2a device that allows only particular types of light or sound to pass through it The camera has an anti-glare filter.
- 3 (computing) a program that stops particular types of electronic information, e-mail, etc. from being sent to a computer