Definition
In a gas turbine engine, exhaust is the high-temperature, high-velocity stream of gases leaving the engine after combustion. The exhaust section directs these gases overboard and, in turbojet and turbofan engines, accelerates them through a nozzle to produce thrust.
Plain English
The hot gases that come out the back of the engine after the fuel has been burned. In a jet, that fast-moving stream pushing out the back is what shoves the airplane forward.
Context Anchor
Seen in gas turbine engine discussions, engine indications, engine fire awareness, and ramp safety around the rear of an operating engine.
Derivation
From the Latin 'exhaurire', meaning 'to draw out' or 'empty out'. The aviation use keeps that original sense — gases being drawn out of the engine after they have done their work.
Why Pilots Care
Exhaust flow produces thrust and its temperature must be monitored to protect the engine from damage.
Intuition Check
Do not read exhaust here as “tired” or “worn out.” In this engine context, exhaust means the hot used gases leaving the engine.
Example Sentence 1
During engine start, the pilot watched the exhaust gas temperature carefully to make sure it stayed within limits.
Example Sentence 2
The pilot watched the exhaust temperature gauge during climb to stay within limits.