Plain English Meaning
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.
Full 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.
Context Anchor
Seen in aircraft systems descriptions for turbine-powered airplanes, especially when learning cabin heat, ventilation, and windshield clearing systems.