infrared

(noun) the infrared region of the electromagnetic spectrum; electromagnetic wave frequencies below the visible range. Synonyms: infrared frequency. Example: "They could sense radiation in the infrared."

(noun) electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves. Synonyms: infrared light, infrared radiation, infrared emission.

(adj) having or employing wavelengths longer than light but shorter than radio waves; lying outside the visible spectrum at its red end. Examples: "Infrared radiation." "Infrared photography."