Echo (acoustics)
In acoustics, echo is when sound comes back. The word echo come from Greek word ἠχώ (ēchō) from (ēchos), "sound".
In nature echo happens in empty spaces, woods or mountains.
Echo (acoustics) Media
Echolocation organs of a toothed whale, which produce echoes and receive sounds. Arrows illustrate the outgoing and incoming path of sound.