Infrared
Electromagnetic radiation whose wavelength is longer than that of visible light (1-750 nm), so that humans cannot see it. It can be used to connect mobile phones to other devices (such as other phones, PDAs, and computers) to exchange information wirelessly. Infrared uses the line-of-sight principle to transmit information using a beam of infrared waves. However, it has largely been replaced by Bluetooth which has longer range and it doesn't require line of sight.
See also Infrared Data Association.
