in·fra·red 
(ĭn′frə-rĕd)
(ĭn′frə-rĕd)adj. Abbr. IR
1. Of or relating to electromagnetic radiation between microwaves and red visible light in the electromagnetic spectrum, having frequencies between 300 gigahertz and 400 terahertz and wavelengths between 1 millimeter and 750 nanometers.
2. Generating, using, or sensitive to infrared radiation.
n.
Infrared light or the infrared part of the spectrum.