Definitions

1. 1.filter (device which separates a suspended, dissolved, or particulate matter from a fluid, solution, or other substance)
2. 2.filter (electronics or software that separates unwanted signals (for example noise) from wanted signals or that attenuates selected frequencies)
3. 3.UV filter
4. 4.filter (non-empty upper set (of a partially ordered set) which is closed under binary infima (a.k.a. meets))