Echo (acoustics)
reflection of sound that arrives at the listener with a delay after the direct sound
In acoustics, echo is when sound comes back. The word echo come from Greek word ἠχώ (ēchō) from (ēchos), "sound".
![](http://up.wiki.x.io/wikipedia/commons/thumb/a/a0/Toothed_Whale_Echolocation.png/220px-Toothed_Whale_Echolocation.png)
In nature echo happens in empty spaces, woods or mountains.