Secondary signal paired with another the primary signal on the main carrier. For example, in satellite television transmission, the video picture is transmitted over the main carrier, and the corresponding audio is sent via an FM subcarrier. Some satellite transponders carry as many as four special audio or data subcarriers whose signals may or may not be related to the main programming.
This is a second signal that "rides" on the main signal with the purpose of carrying additional information. In satellite TV transmissions, for example, the video is transmitted by the main carrier signal, and the audio information is relayed by an FM subcarrier.
Secondary carrier sent within a radio channel carrying either supplemental information to the main signal or totally separate programming or data. Stereo sound is sent on a subcarrier and when it is part of a TV signal it is called MTS stereo. A TV subcarrier with a totally different audio source from the main TV channel is called a Secondary Audio Program (SAP). According to ECPA, subcarriers may not be monitored without the permission of the sender.