- A porous device for removing impurities or solid particles from a liquid or gas passed through it
- (filter) remove by passing through a filter; "filter out the impurities"
- A screen, plate, or layer of a substance that absorbs light or other radiation or selectively absorbs some of its components
- (filter) an electrical device that alters the frequency spectrum of signals passing through it
- (filter) device that removes something from whatever passes through it
- A device for suppressing electrical or sound waves of frequencies not required