Throttle levers are controls found in various vehicles, including aircraft, boats, and cars, that regulate the engine's power output. By adjusting the position of the throttle lever, the operator can increase or decrease the amount of fuel and air mixture entering the engine, which directly affects speed and acceleration. In aircraft, throttle levers are typically located in the cockpit and are used to manage engine thrust during different phases of flight. In cars, they are often part of the accelerator pedal system, allowing drivers to control their speed smoothly and efficiently.