A satellite is defined by the National Aeronautics and Space Administration (NASA) as an object that moves around a larger object.
This applies to planes, moons, and other 'natural' satellites. However, when talking about satellites, most will think of the man-made objects that orbit Earth.
According to NASA, there are thousands of man-made satellites. Some take pictures of planet Earth, others take pictures of other planets, the sun and other objects.
Other satellites send TV signals, help understand the weather, send navigation signals, phone calls/telecommunication signals, etc.