A satellite is something that orbit a bigger object like a machine, planet or moon that revolves around a star or planet. There are natural satellites like planets or moons and artificial satellites like man made objects that revolve earth.
The matter I am concern here is artificial satellite. It is build usually for a specific purpose. It can be for research, communications, weather, navigation, military and etc.
The satellites can be in low-Earth orbit(160km from earth surface), medium-Earth orbit (20,000km from earth surface) and geostationary orbit (36,000km).
It is estimated about 6,600 satellites have been launched. The latest count is 3,600 satellites still remain in orbit. Only 1,000 are operational.
The first artificial satellite is Sputnik 1 launched in 1957 by the Russians. (Credit:space.com & en.wikipedia.org/wiki/Satellite)