When water waves strike a barrier straight on, they reflect back along the same path.
When incident waves strike a parabolic surface, the waves reflect to a focal point.
When incident waves strike a barrier at an angle they reflect off at the same angle. The Normal (N) is a line drawn perpendicular to the barrier/surface the wave hits. The normal line intersects the surface at the identical point the wave hits the barrier/surface. The Angle of Incidence, θ i, of a wave is the angle measured from the incident wave (i) to a line normal to the barrier/surface. The Angle of Reflection, θ r, of a wave is the angle measured between the reflected wave (r) and a line normal to the barrier/surface.
The Angle of Incidence is equal to the Angle of Reflection