In physics, the infrared radiation (IR) is electromagnetic radiation with a frequency band of the electromagnetic spectrum than that of visible light, but greater than that of radio waves, or a wavelength between 700 nm and 1 mm (infrared band) .
The term means "below red" because red is the color visible with the lowest frequency.
It is often associated with the concepts of "heat" and "heat radiation" because every object with a temperature above absolute zero (basically any real object) spontaneously emits radiation in this band (for the Wien law increasing the temperature peak emission moves more and more towards the visible until the object becomes incandescent).
