ffiilltteerr -- Definition

A _f_i_l_t_e_r  is a  program that reads  a stream of  input, transforms it  in a
precisely defined  manner, and  writes it to  another stream.  Two  or more
filters can be coupled with _p_i_p_e_s  to perform a complex transformation on a
stream of input.

_S_e_e _A_l_s_o
ppiippee, UUssiinngg CCOOHHEERREENNTT
