A multicore cable is a generic term for an electrical cable that has multiple cores made of copper wire. The term is normally only used in relation to a cable that has more cores than commonly encountered. For example, a four core mains cable is never referred to as multicore, but a cable comprising four coaxial cables in a single sheath would be considered multicore.
Multicore cables are used with professional video cameras. In television studios, 26-pin cables are used to connect "cameras" to camera control units (CCU). Triaxial cables are used primarily in outside broadcasting however both are capable of delivering an HD-SDI feed and 30 - 40 Watts of power for the Cameras.