A satellite is an object that orbits around a celestial body. Earth is a satellite of the Sun, which is a satellite of the Milky way. Man-made satellites can facilitate telecommunications or serve other functions.
An example of a man-made satellite is a radio relay station that orbits the earth. A complete satellite communications system also includes earth stations that communicate with each other via the satellite. The satellite receives a signal transmitted by an originating earth station and retransmits that signal to the destination earth station(s). Satellites are used to transmit telephone, television and other data signals originated by common carriers, broadcasters and distributors of cable television program material. Weather satellites are used to image and observe the earth's weather to aid meteorologists with weather forecasting.
US spy satellite fleet
The US invested vast sums of money into high-altitude research—from early "weather balloons" to the SR-71 Blackbird and U2 Dragon Lady to orbital telescopes—and established not one but three Federal agencies—the National Reconnaissance Office (NRO), the National Security Agency (NSA), and the Central Intelligence Agency (CIA)—all in an effort to glean any speck of information that could give the US an advantage. Satellite technology is, by far, the most expensive ISR method at the US's disposal but also the most effective.