Look up orifice in Wiktionary, the free dictionary.

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 controversial computer program designed for remote system administration