A secondary telecommunications channel that resides within the main channel (a carrier within a carrier). A type of multiplexing, the subcarrier is a modulated carrier signal at a lower frequency that is combined with the main carrier signal running at a higher frequency.
Color TV signals were added in a subcarrier to black and white signals in order to maintain backward compatibility with monochrome TV sets. Stereo was added to FM radio in a subcarrier for compatibility. Subcarriers are also often used to provide the audio channel in a video broadcast. See carrier