(1) A transmit/receive device; a transceiver. The term may refer to the entire unit or only to the circuits that do the actual transmitting and receiving. The phrase "the device has two radios" means the unit has two transmitters or two transceivers.

(2) The transmission of electromagnetic radiation (energy) through the air or through a hollow tube called a "waveguide." Although radio is often thought of as only AM and FM radio or sometimes two-way radio, all transmission systems that propagate signals over the airwaves are called "radio," including TV, satellite, portable phones, cellphones and wireless LANs. See spectrum.