An engine is a machine that converts energy into motion and mechanical work. Most engines burn fuel like gasoline or diesel to create the power that moves cars, trucks, airplanes, and ships. When you start a car, the engine begins a rapid series of tiny explosions inside its cylinders, and that power turns the wheels. Jet engines work differently: they suck in air, compress it, mix it with fuel, and blast it out the back to push planes forward at incredible speeds.

Before gasoline engines, the first engines were steam engines, which burned coal or wood to heat water into steam. That pressurized steam pushed pistons back and forth, powering everything from locomotives to factory machines. Steam engines launched the Industrial Revolution in the 1700s and 1800s, transforming how people manufactured goods and traveled.

The word can also describe someone who powers a group effort. A hardworking student might be the engine that keeps a group project moving forward, just like a literal engine keeps a train chugging down the tracks. Similarly, we might say that a city's economy is powered by a particular industry that serves as its economic engine.