Plain English Meaning

To let the higher-pressure air inside the cabin out, so the inside and outside pressures match.

Full Definition

To deliberately reduce the air pressure inside a pressurized aircraft cabin so it equals the outside ambient pressure. This is done by opening outflow valves, shutting off pressurization air sources, or climbing/descending to an altitude where the pressure differential is zero.

Context Anchor

Seen in emergency procedures for pressurized airplanes, including smoke, fire, and cabin-pressure problems.

Derivation

Built from 'de-' (Latin, meaning 'remove' or 'undo') and 'pressurize' (to add pressure). So it literally means 'to undo the pressurization' — to take the added pressure back out.