Definition
A cabin heating system used in turbine-powered aircraft that draws hot, high-pressure air from the compressor section of the engine and routes it, after temperature regulation and mixing with cooler air, into the cabin to provide warmth.
Plain English
It heats the cabin by tapping a small amount of hot air from the engine's compressor and piping it inside, cooled down to a comfortable temperature before it reaches the passengers.
Context Anchor
Seen in aircraft systems descriptions for turbine-powered airplanes, especially when learning cabin heat, ventilation, and windshield clearing systems.
Derivation
Bleed' here means to draw off or tap a small amount from a larger supply, the same way you might bleed pressure from a hydraulic line. The engine compressor produces far more compressed air than it needs for combustion, so a portion is 'bled off' and put to use elsewhere -- in this case, heating the cabin.
Why Pilots Care
Provides reliable cabin heat and defogging without adding significant weight or complexity.
Analogy
Like tapping heat from a car engine to warm the passenger compartment instead of using a separate heater.
Intuition Check
Do not read “bleed air” as an accidental air leak. In this term, “bleed” means air intentionally taken from the engine for a useful aircraft function.
Example Sentence 1
Before takeoff, the crew confirmed the bleed air heating system was selected on so the cabin would warm up during the climb.
Example Sentence 2
During the flight the instructor showed how the bleed air heating system also supplies warm air to the rear seats.