Throttle

A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.

An engine's power can be increased or decreased by the restriction of inlet gases (i.e., by the use of a throttle), but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated. What is often termed a throttle (in an aviation context) is more correctly called a thrust lever, particularly for jet engine powered aircraft. For a steam engine, the steam valve that sets the engine speed/power is often known as a regulator.

Internal combustion engines

In a gasoline internal combustion engine, the throttle is a valve that directly regulates the amount of air entering the engine, indirectly controlling the charge (fuel + air) burned on each cycle due to the fuel-injector or carburetor maintaining a relatively constant fuel/air ratio. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle pedal, as it controls the throttle opening, although "accelerator pedal" is more accurate, since not all vehicles have throttles. A diesel engine does not have a throttle; its power level is controlled by regulating the fuel flow into the engine, thus "throttle" and "gas pedal" are both inaccurate terms when applied to a diesel engine.