Subcarrier

A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth. This is an early and simple method of multiplexing.

Read more about Subcarrier:  FM Stereo, Television, Private Audio, Datacasting, Telemetry and Foldback, MCPC Satellites