Definition
A movable disc or butterfly valve in the carburetor or induction system that controls the volume of the fuel/air mixture flowing into the engine, and therefore controls engine power output. The valve is operated by the throttle control in the cockpit.
Plain English
A round flap inside the carburetor that opens and closes when you move the throttle. The more it opens, the more fuel and air reach the engine, so the engine produces more power.
Context Anchor
Seen in carburetor system descriptions and when learning how the cockpit throttle controls power on a carbureted piston engine.
Derivation
The word 'throttle' comes from an old English word meaning 'throat,' because the valve sits in the throat of the induction passage and squeezes or opens that passage to control flow.
Why Pilots Care
Directly determines engine RPM and power output; correct operation is essential for takeoff, climb, cruise, and landing performance.
Analogy
It works like a door in a hallway: open the door wider and more can pass through; close it and less can pass through.
Intuition Check
Do not think of the throttle valve as a fuel-only valve. In a carbureted engine, it mainly controls the flow of the air-and-fuel mixture going into the engine.
Example Sentence 1
As the pilot advanced the throttle for takeoff, the throttle valve opened fully, allowing maximum fuel/air mixture into the engine.
Example Sentence 2
During the approach the pilot reduced throttle, partially closing the throttle valve to lower engine power.