It had referred to a city-state. Here is why:
A polis is a city-state in ancient Greece. Usually it had consisted of a little village sort of place that was in the polis. The polis had contained a hill that a sort of palace sat on called an acropolis. It was usually built by the sea.
Well hope that helped a bit!
Sorry if you don't understand it because you didn't learn it yet. I hope that you understand it better when the teacher goes over it. I also have put a diagram so you can see the polis better.