1. [n]  the infrared part of the electromagnetic spectrum; electromagnetic wave frequencies below the visible range; "they could sense radiation in the infrared"
2. [n]  electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves
3. [adj]  having or employing wavelengths longer than light but shorter than radio waves; lying outside the visible spectrum at its red end; "infrared radiation"; "infrared photography"

(IR) Electromagnetic waves in the frequency range just below visible light corresponding to radiated heat. IR waves can be generated by a kind of LED and are often used for remote controls for televisions etc. and in some docking stations.