Orifice
Water
An opening with a closed perimeter and a regular form through which water flows. If the perimeter is not closed or if the opening flows only partially full, the orifice becomes a weir.
(1) An opening with closed perimeter, usually sharp edged, and of regular form in a plate, wall, or partition through which water may flow, generally used for the purpose of measurement or control of water. (2) The end of a small tube, such as a Pitot tube, piezometer, etc.
- — Service Hydrologist Reference Manual Glossary of Hydrologic Terms retrieved 2014-06-01
Weather
In hydrologic terms,
(1) An opening with closed perimeter, usually sharp edged, and of regular form in a plate, wall, or partition through which water may flow, generally used for the purpose of measurement or control of water.
(2) The end of a small tube, such as a Pitot tube, piezometer, etc.