Definition
The reduction of pressure inside a sealed volume, most commonly the loss of cabin pressure in a pressurized aircraft. Decompression can be slow (a gradual leak through a faulty seal or valve) or rapid (a sudden structural failure such as a window or door losing integrity), and it exposes occupants to the lower ambient pressure of the surrounding atmosphere.
Plain English
The pressure inside the cabin drops, either slowly or suddenly, until it matches the thinner air outside the aircraft.
Context Anchor
Seen in high-altitude operations, pressurization system discussions, oxygen-mask procedures, and emergency descent checklists.
Derivation
From Latin 'de-' (removal, reversal) and 'compressio' (a pressing together). Decompression is literally the undoing of compression — releasing pressure that was being held in.
Why Pilots Care
Uncontrolled decompression can cause hypoxia, requiring immediate oxygen use and descent to prevent incapacitation.
Analogy
It is like opening a sealed bag of chips at altitude: once the pressure difference has a way out, the air inside and outside try to equalize. In an aircraft cabin, that pressure change matters because people are depending on the cabin pressure to breathe normally.
Grounding Statement
At high altitude, decompression means the protective air pressure inside the aircraft is being lost.
Intuition Check
Decompression does not mean relaxing after stress here. It means a drop or loss of air pressure inside the aircraft cabin.
Example Sentence 1
After the cabin door seal failed, the crew experienced a slow decompression and began a controlled descent to a lower altitude.
Example Sentence 2
A slow decompression from a small leak may go unnoticed until symptoms of hypoxia appear.