Definition
A nozzle in which the gas flowing through it has reached the speed of sound at the narrowest point (the throat). Once this condition is met, the mass flow through the nozzle cannot be increased by further lowering the downstream pressure; the flow is said to be choked.
Plain English
A nozzle running so fast that the gas inside it has hit the speed of sound at its tightest spot. After that point, no matter what you do at the exit end, you can't push any more gas through it per second.
Context Anchor
Seen in turbine engine and exhaust system discussions, especially when describing airflow, exhaust flow, thrust, and pressure changes through a nozzle.
Derivation
Choked' comes from the everyday sense of a passage being so restricted that nothing more can get through. In gas dynamics it carries that same idea: the throat has reached a flow limit it cannot exceed.
Why Pilots Care
Limits maximum engine airflow and thrust output once sonic conditions are reached at the throat.
Grounding Statement
Picture exhaust gas rushing through a narrow opening so fast that it reaches its maximum possible flow rate for the existing pressure and temperature.
Intuition Check
“Choked” does not mean the nozzle is plugged. Here it means the flow has reached a maximum-rate condition because the gas is moving at the speed of sound at the narrowest point.
Example Sentence 1
At full throttle in the climb, the engine's exhaust nozzle was choked, so further reductions in outside pressure produced no increase in mass flow.
Example Sentence 2
Engineers adjusted the nozzle geometry to delay choked flow until higher Mach numbers.