In the context of wave behavior, what does 'angle of incidence' refer to?

The term 'angle of incidence' specifically refers to the angle at which a wave approaches and strikes a surface, such as when light hits a mirror or sound waves meet a wall. This angle is measured relative to the normal, which is an imaginary line perpendicular to the surface at the point of incidence. The angle of incidence is critical in various wave phenomena, including reflection and refraction, as it helps determine how the wave behaves once it interacts with the surface. Understanding this concept is foundational in fields like optics and acoustics, where the behavior of waves significantly impacts practical applications.