A generic term for radio-based technology and is usually referred to whenever a signal is radiated through the air. It is the portion of the electromagnetic spectrum with frequencies between 3 kHz and 300 GHz. This corresponds to wavelengths between 30 kilometers and 0.3 millimeter. The international unit for measuring frequency is Hertz (Hz), which is equivalent to the older unit of cycles per second. One Megahertz (MHz) is one million Hertz. One Gigahertz (GHz) is one billion Hertz. For reference: the standard US electrical power frequency is 60 Hz, the AM broadcast radio frequency band is 0.55 -1.6 MHz, the FM broadcast radio frequency band is 88-108 MHz, and microwave ovens typically operate at 2.45 GHz. Typically RF are frequencies from 20 kHz to 3 GHz. Literally, any and all frequencies that can be radiated as an electromagnetic wave.