infrared

Short definition from Wiktionary

Noun

1. 1
   The electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation, having a wavelength between 700 nm and 1 mm.
2. 2
   A specific wavelength in this range.
3. 3
   A device that emits infrared radiation.

Adjective

1. 1
   Having a wavelength in the infrared spectrum.
2. 2
   Relating to very low energies or very large distances or time spans.