To release or reduce the pressure of a gas or liquid in a container or system. The technician had to depressurize the tank before performing maintenance.
To lower the air pressure in an aircraft cabin to match the outside atmospheric pressure. In an emergency, the pilot may need to depressurize the cabin quickly.
To lose internal pressure; to undergo a reduction in pressure, especially suddenly and unintentionally. After the valve failed, the vessel began to depressurize rapidly.