Short for InfraRed. An invisible band of radiation at the lower end of the electromagnetic spectrum. It has beginnings in the middle of the microwave spectrum and goes up to an ambiguous area at the beginning of visible light. Infrared transmission requires a totally clear line of sight between transmitter and receiver. It is used for wireless transmission between computer devices and PDAs as well as most all current remote units for televisions, video devices and both home and mobile stereo equipment. See IrDA.