Throttle is a control device that regulates how much fuel and air flow into an engine, which controls the engine's power and speed. When you push down the gas pedal in a car, you're opening the throttle to let more fuel and air in, making the engine work harder and the car go faster. When you ease off the pedal, you're closing the throttle, which slows the car down. Motorcycles have twist-grip throttles on the handlebar: twist forward to go faster, twist back to slow down.

As a verb, people sometimes say they need to throttle back their plans or efforts, meaning to slow down or reduce intensity. A teacher might tell an overly ambitious student to throttle back and focus on finishing one project well before starting three more. In computer systems, internet providers sometimes throttle connection speeds during peak hours, deliberately slowing things down to manage network traffic.