In modern times, what Aristotle called a “polis” has developed into the state – an independent political unit.  Most often states are called “nation” or “country” or “nation-state.”
During your time studying government in this course, this use of the term “state” should not be confused with the term as it applies to those sub-governments within the United “States” of America.  In the early days of this nation, each of the original 13 states was actually its own mini-nation, with all of the powers of independent states.  However, with the ratification (legal acceptance) of the Constitution in 1787, the term “state” came to mean a smaller part of the U.S.A. – but such states are now under the over-all sovereignty of the national, or U.S. government, and are no longer entirely independent of the rest of the nation.