Reflection is the change in direction of a wave front at an interface between two different mediums so that the wave front returns into the medium in which it originated. Common examples of this include the reflection of light, sound and water waves. In acoustics, reflection causes echoes. This is why when you go to a school concert, there are those white barriers behind the performers. They are there to reflect the sound from coming from the instruments to the crowd. Acoustics also play an important role in understanding how waves behave because the angle in which the waves hit the acoustics walls, the angle remains the same as it bounces off the acoustics barrier.