Electromagnetic radiation
From The Glossary of Digital Photography
Energy made up of two parts: magnetic and electric. This energy occurs in waves that are in right angles to each other. There are different types of electromagnetic radiation depending on the frequency of their waves. These include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma rays. Digital photography is mainly concerned with visible light and, in some cases, infrared radiation.
