An echo is a sound that bounces back to you after hitting a surface like a wall, cliff, or the side of a building. When you shout “hello!” in a canyon and hear “hello!” come back a moment later, that's an echo. The sound waves from your voice travel outward, strike the canyon walls, and reflect back to your ears, just like a ball bouncing off a wall.

Echoes happen when you're far enough from the reflecting surface that you can hear the original sound and the bounced-back sound as separate events. In a small room, sounds bounce around too quickly to create distinct echoes. But in a large empty gym or a mountain valley, the delay creates that ghostly repetition effect.

The word also describes repeating or imitating something that came before. When a student's essay echoes ideas from a famous speech, it reflects those same thoughts. If your friend constantly echoes whatever the popular kids say, they're repeating others instead of thinking for themselves. A news report might echo earlier stories on the same topic, covering similar ground.

Nature uses echoes in fascinating ways. Bats and dolphins navigate using echolocation, sending out sound waves and listening for the echoes to map their surroundings in darkness or murky water.