When you were a kid, you likely enjoyed yelling your name in a place, such as a valley, where you could anticipate hearing your name repeated back to you in an echoing form. Unlike reverberations, an echo takes longer to return back to our hearing. The sound is not altered or added to, but instead repeated after bouncing off a hard surface such as a wall.
Anytime you hear an echo, the repeated noise sounds like a fainter version of the original utterance or noise. You can measure an echo based on the number of seconds that pass between each repeated sound.