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 Echo is an acoustic phenomenon where sound is reflected back to the listener. It is created when sound waves travel away from the source and then bounce off a surface, such as a wall or a mountain, and return to the listener. Echoes can be heard in many places, such as in a canyon, a cave, or a large room. Echoes can also be heard in nature, such as when a bird call is reflected off a cliff face. Echoes can be used to measure the distance of an object, such as a mountain, by timing how long it takes for the sound to return. Echoes can also be used to locate objects, such as a submarine, by listening for the sound of its engine. Echoes can also be used to create special effects in music, such as reverb, which is a type of echo that is created by repeating a sound multiple times. Echoes can also be used to create a sense of space in a recording, such as a concert hall or a cathedral.