What does "fricative" mean?

Fricative: Produced by the friction or rustling of the breath, intonated or unintonated, through a narrow opening between two of the mouth organs; uttered through a close approach, but not with a complete closure, of the organs of articulation, and hence capable of being continued or prolonged; -- said of certain consonantal sounds, as f, v, s, z, etc. -- n. A fricative consonant letter or sound. See Guide to Pronunciation, §§ 197-206, etc.