infrared(n = noun.attribute) infrared frequency - the infrared region of the electromagnetic spectrum; electromagnetic wave frequencies below the visible range; "they could sense radiation in the infrared"
Lying outside the visible spectrum at its red end; -- said of rays having a longer wavelength (and thus less refrangible) than the extreme red rays, specifically those electromagnetic waves having a wavelength of between 700 nanometers and 1 millimeter. [Webster 1913 Suppl.]
relating to, using, or producing infrared radiation. [PJC]
affected by infrared radiation; as, infrared detector; infrared film. [PJC]
infrared, adj.
1 having a wavelength just greater than the red end of the visible light spectrum but less than that of radio waves.
2 of or using such radiation.