An orifice is any opening, mouth, hole or vent, as in a pipe, a plate, or a body
Body orifice, any opening in the body of a human or animal Orifice plate, a restriction used to measure flow or to control pressure or flow, sometimes given specialised names: Calibrated orifice, used to control pressure or flow Restrictive flow orifice, used to control flow Miss Shilling's orifice, used to control flow in the engines of early Spitfire and Hurricane fighter aeroplanes Back Orifice, a tendentious computer program designed for remote system administration
See also Choked flow Needle valve Nozzle Venturi effect Flow measurement