|filter /ˈfɪltɚ/ noun [count]|
1 : a device that is used to remove something unwanted from a liquid or gas that passes through it • She smokes cigarettes withfilters. • a water filter
2 : a device that prevents some kinds of light, sound, electronic noises, etc., from passing through • He placed a red filter on the camera lens. • digital filters that stop high-frequency sounds
3 computers : software that prevents someone from looking at or receiving particular kinds of material through the Internet • a spamfilter [=a program that keeps you from seeing spam or unwanted e-mail]
Learn about filter as a verb.