A satellite is a celestial companion. It usually refers to the companions that orbit our Earth far up in the sky. The moon is a natural satellite of the earth. Much smaller are the artificial satellites: Humans have launched them into space with rockets. The word satellite comes from the Latin language and means "companion".
Artificial satellites have been around since 1957, and since then several hundred of them have been constantly orbiting the Earth. Many of them rotate directly with the Earth and can therefore always be seen in the same place in the sky with a powerful telescope. Some observe the Earth or space for us. Others are there to carry television programmes, telephone calls and other things from place to place.