f/ /v/ labiodental fricatives
A labiodental (from labia lip and dental teeth) fricative is a sound in which the flow of air out of the body is constricted by upper teeth to the lower lip, creating turbulence for the air, but not stopping its passage out of the mouth. English has two labiodental fricatives — /f/ in which the vocal chords are not used (voiceless) as in fire and laughter, and /v/ in which they are used as in very and of.