Optics is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. Optics explains optical phenomena.

The field of optics usually describes the behavior of visible, infrared, and ultraviolet light; however because light is an electromagnetic wave, analogous phenomena occur in X-rays, microwaves, radio waves, and other forms of electromagnetic radiation. Optics can thus be regarded as a sub-field of electromagnetism.