Definition 1 of 2
Plain English Meaning
The window of time you have at altitude, after your oxygen supply fails, to still think clearly enough to fix the problem before hypoxia takes over.
Full Definition
The amount of time a pilot has, after a loss of adequate oxygen at altitude, to recognize the problem and take corrective action before mental and physical performance degrade to the point where useful tasks can no longer be performed. It shortens dramatically with increasing altitude and with rapid decompression.
Context Anchor
Seen in high-altitude flying, oxygen-use training, and discussions of hypoxia in the Pilot’s Handbook of Aeronautical Knowledge.