To most of us the planets just seem to go across the sky with the stars, in a 24-hour cycle, as the earth spins. But the planets are moving, against the background of stars.
Planet means wanderer in Greek.
If you map a planet's apparent path through the stars, you will see it appear to stop and go backward, every once in a while. The triumph of Copernicus' theory of a sun-centered solar system was that it explained retrograde motion quite simply. On the left we see two planets orbiting the sun. We are on the blue planet, looking at the red planet. This is just because we are speeding past the other planet.