Definition of "Valve" :

noun: one of the paired hinged shells of certain molluscs and of brachiopods

noun: the entire one-piece shell of a snail and certain other molluscs

noun: control consisting of a mechanical device for controlling the flow of a fluid

noun: device in a brass wind instrument for varying the length of the air column to alter the pitch of a tone

noun: a structure in a hollow organ (like the heart) with a flap to insure one-way flow of fluid through it