Radiant energy, also known as electromagnetic radiation, is the energy emitted by any substance with a temperature above absolute zero. Some synonyms for radiant energy include light, heat, radiation, electromagnetic waves, and radiant heat. Light is commonly used to refer to the visible portion of the electromagnetic spectrum. Heat describes the infrared portion of the spectrum, while radiation is a general term that encompasses all forms of electromagnetic radiation. Electromagnetic waves are a form of energy that propagate through space and can be divided into different bands, such as radio waves and X-rays. Radiant heat is the transfer of energy through radiation. All of these terms are used interchangeably with radiant energy and are widely used in physics.