1. The use of electromagnetic radiation of frequency within the radiofrequency portion of the electromagnetic spectrum (see frequency band) for the transmission and reception of electrical impulses or signals without connecting wires or waveguides. It is also the process of transmitting or receiving such signals.
The unqualified term usually denotes the telecommunication system that transmits audio information. Any communication channel, circuit, or link in which information is transmitted by radio is described as a radiocommunication or radio channel, radio circuit, or radio link.
2. Short for radiofrequency. Denoting electromagnetic radiation in the radiofrequency range or any device, component, or other apparatus used to transmit or receive information at frequencies within this range, as in radio telephony, radio telemetry, or radio astronomy.