To rev means to make an engine run faster while the vehicle stays still, creating that distinctive roaring sound you hear when someone presses the gas pedal without moving. Mechanics rev engines to test them, and drivers rev engines to warm them up on cold mornings. You might see a motorcyclist revving their engine at a stoplight, or hear a race car driver rev the engine before the starting flag drops.

People also use rev more broadly to describe building up energy or intensity: a coach might try to rev up the team before a big game, or you might feel revved up with excitement before your birthday party.

In racing, drivers carefully control how much they rev their engines to get maximum power without damaging anything. Rev too little and you won't accelerate quickly; rev too much and you might blow the engine. It takes skill and experience to know just how much to rev.