(uncountable) The electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation, having a wavelength between 700 nm and 1 mm.
(countable) A specific wavelength in this range.
(countable) A device that emits infrared radiation.
Having a wavelength in the infrared spectrum.
(figurative, physics) Relating to very low energies or very large distances or time spans.