Infrared (IR) radiation is a type of electromagnetic radiation (a wave with electricity) . The wave is longer than light which humans can see and shorter than microwaves. The word "infrared" means "below red". It comes from the Latin word "infra" (meaning "below") and the English word "red". (Infrared light has a frequency "below" the frequency of red light.) Red light has the longest wavelength that human eyes can see. Infrared waves cannot be seen by the eye. 