A communications satellite (sometimes abbreviated to SATCOM) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbit, other elliptical orbits and low ( polar and non-polar) Earth orbits.
For fixed ( point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of submarine communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting, for which application of other technologies, such as cable, is impractical or impossible
A spacecraft in orbit around the Earth to receive and retransmit radio signals. Communications satellites amplify and sort or route these signals. In earlier days they functioned much like ground microwave repeaters but with greatly increased coverage. Whereas a ground repeater relays signals between two fixed locations, a communications satellite interconnects many locations, fixed and mobile, over a wide area. With the advent of on-board processing, switching and rerouting of signals has been added to the functionality of some communications satellites, making them “switchboards in the sky.”