1fil·ter 
/ˈfɪltɚ/ noun
plural fil·ters /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 with filters. ▪ 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 spam filter [=a program that keeps you from seeing spam or unwanted e-mail]
▪ She smokes cigarettes with filters. ▪ a water filter
▪ He placed a red filter on the camera lens. ▪ digital filters that stop high-frequency sounds
▪ a spam filter [=a program that keeps you from seeing spam or unwanted e-mail]
