To bang means to hit or strike something hard, making a loud noise. When you bang a drum, you hit it forcefully. When a door slams shut in the wind, it bangs against the frame. You might bang your knee on the coffee table while running through the living room, which hurts and probably makes a thudding sound.

The word also describes the loud sound itself. A firecracker makes a bang when it explodes. Thunder creates a tremendous bang during a storm. When something happens suddenly and dramatically, people sometimes describe it as happening with a bang: “The fireworks show ended with a bang.”

In science, the Big Bang is the name for the moment about 14 billion years ago when the universe began expanding from an incredibly hot, dense point. Scientists chose this name because they imagined it as a massive explosion, though it actually didn't make any sound because there was no air to carry sound waves yet.

You might also hear bang used as an exclamation, like a comic book sound effect: “Bang! Pow!” When someone does something with great energy or enthusiasm, they're really banging away at it, like a carpenter banging nails into wood all day long.