reflection, abrupt change in the direction of propagation of a wave that strikes the boundary between different mediums. At least part of the oncoming wave disturbance remains in the same medium. Regular reflection, which follows a simple law, occurs at plane boundaries.
Reflected waves return immediately to their original medium instead of entering the medium they encounter. ♦ According to the law of reflection, the angle of reflection of a reflected wave is equal to its angle of incidence.