The Collaborative International Dictionary of English v.0.48:

Infrared Radiation \In`fra*red" Ra`di*a"tion\, n. [Infra- +
   red.] (Physics)
   electromagnetic radiation having a wavelength of between 700
   nanometers and 1 millimeter.

   Note: Infrared radiation is that electromagnetic radiation
         lying between the visible spectrum and the longest
         microwaves. It may be absorbed by matter in a manner
         specific to the absorbing substance, causing increased
         vibration of molecules. The infrared absorption
         spectrum of a chemical compound is often very specific,
         and the infrared absorption spectrum is therefore used
         to help identify chemical substances. Infrared
         radiation is used in certain communication devices,
         such as television remote controls and communication
         devices between computers or between computers and
         peripherals.
         [PJC]

WordNet (r) 3.0 (2006):

infrared radiation
    n 1: electromagnetic radiation with wavelengths longer than
         visible light but shorter than radio waves [syn:
         infrared, infrared light, infrared radiation,
         infrared emission]