How would I explain federalism to somebody?

Federalism is a system of government in which power is divided between a central authority (the national government) and smaller political units (such as states or provinces). In a federal system, both levels of government have their own areas of authority and responsibility, and they operate independently of each other while still remaining interdependent. This system helps to balance the power between the national government and the regional governments, allowing each level to make decisions on specific issues that affect their respective populations. Federalism also promotes diversity and individuality within a country by allowing different regions to have their own laws, policies, and political systems.