A surface that (a) serves as a boundary between two dissimilar propagation media, such as media with different refractive indices, and (b) has the ability to change the direction of incident waves, such as electromagnetic waves, sound waves, or water waves. Note 1: Propagation media include free space and material media. Note 2: If all the incident wave power is transmitted through, or is absorbed at, a surface, it is not a reflecting surface. See also absorption,  electromagnetic wave,  free space,  incident,  interface,  interface surface,  power,  propagation medium,  real surface,  refractive index,  sound wave,  transmit,  wave.