Infra-red is a term used to describe a type of electromagnetic radiation that has a wavelength longer than visible light. There are several synonyms for the word infra-red that can be used interchangeably. These include infrared radiation, thermal radiation, heat radiation, and IR radiation. Infrared radiation is commonly used in a variety of applications such as in remote controls, temperature sensors, and medical imaging. Thermal radiation refers to infrared radiation that is emitted by objects based on their temperature. Heat radiation is another synonym used to describe the phenomenon whereby radiant energy is emitted by a body due to its temperature. IR radiation is simply an abbreviation of infrared radiation.