Geometrical optics, or ray optics, describes the propagation of light in terms of "rays" which travel in straight lines, and whose paths are governed by the laws of reflection and refraction at interfaces between different media.
Ray optics, or geometrical optics, is based on the short-wavelength approximation of electromagnetic theory. It is defined in terms of a package of rules (the rules of geometrical optics) that can be arrived at from the Maxwell equations in a consistent approximation scheme~
