A material or device that allows certain substances to pass through it, while keeping other substances out. Filters may be used in cigarettes to help trap tar and other harmful substances found in tobacco smoke. In medicine, filter also means to remove toxins, poisons, or other harmful substances from the blood. For example, the kidneys remove waste and extra water from the blood (as urine). The liver also removes harmful substances from the blood.
Source: NCI Dictionary of Cancer Terms2013-07-18 Date last modified: 2015-08-13