Political science is the systematic study of politics and political systems. It examines areas like public policy, political theory, and international relations. The word "politics" derives from the Ancient Greek word "polis" meaning city-state. A state has four key elements - a people, a territory, a government, and sovereignty. It is distinguished from a nation, which is an ethnic concept, and from a government, which can change while the state remains the same as long as its essential elements are still present. The study of political science aims to educate citizens and provide an understanding of how government works.