• An airtight chamber such as that used in tunnel and caisson excavation.
  • A system of double doorways permitting entry and exit while preventing airflow from one area to another, as from a contaminated area to an uncontaminated area.
  • An entrance room between areas of different pressures, such as the entrance to an air-supported structure.
  • In plumbing, air trapped in a system and preventing flow.

Real Estate

  • noun an obstruction to the flow of a liquid in a pipe, caused by a bubble of air