An echo is caused when sound waves bounce off of a surface and travel back to the ears. Echoes commonly occur when loud sounds are emitted into an empty room or down a well. The echo occurs when sound is reflected off water in the well or walls in rooms.
An echo is a delayed sound, and a true echo is a singular reflection of a primary sound. The amount of time between when the sound is emitted and when the echo is heard is determined by the distance between the surface that reflects the sound and the object emitting the sound.