Reflection of sound waves off of barriers result in some observable behaviors which you have likely experienced. If you have ever been inside of a large canyon, you have likely observed an echo resulting from the reflection of sound waves off the canyon walls. Suppose you are in a canyon and you give a holler. Shortly after the holler, you would hear the echo of the holler - a faint sound resembling the original sound. This echo results from the reflection of sound off the distant canyon walls and its ultimate return to your ear. If the canyon wall is more than approximately 17 meters away from where you are standing, then the sound wave will take more than 0.1 seconds to reflect and return to you. Since the perception of a sound usually endures in memory for only 0.1 seconds, there will be a small time delay between the perception of the original sound and the perception of the reflected sound. Thus, we call the perception of the reflected sound wave an echo.

Source: https://www.physicsclassroom.com/mmedia/waves/er.cfm