1. (noun)infrared, infrared frequency the infraredregion of the electromagnetic spectrum; electromagnetic wave frequencies below the visible range "they could sense radiation in the infrared"
2. (noun)infrared, infrared light, infrared radiation, infrared emission electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves
3. (adj)infrared having or employing wavelengths longer than light but shorter than radio waves; lyingoutside the visible spectrum at its red end
"infrared radiation"; "infrared photography"