A federation is a union of a number of self-governing states or regions, which are joined together under a central government. The central government is not able to do a lot of things that central government in more centralized states can. These things are done by the states (or regions) in a federalized state.

The United States of America is a federation. The federal (central) government has the highest executive role, but the states have their own special rules in some special cases.

Australia became a Federation in 1901.

After the 1971 civil war, Pakistan became a Federation adopted in the 1973 Constitution of Pakistan.

Other examples of federal states are Austria, Belgium (since 1993), Canada, Germany, Russia and Switzerland.