A U.S. state is any one of the 50 federated states of the United States of America

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 that share sovereignty

Sovereignty

Sovereignty is the quality of having supreme, independent authority over a geographic area, such as a territory. It can be found in a power to rule and make law that rests on a political fact for which no purely legal explanation can be provided...

 with the federal government

Federal government of the United States

The federal government of the United States is the national government of the constitutional republic of fifty states that is the United States of America. The federal government comprises three distinct branches of government: a legislative, an executive and a judiciary. These branches and...

. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile

Domicile (law)

In law, domicile is the status or attribution of being a permanent resident in a particular jurisdiction. A person can remain domiciled in a jurisdiction even after they have left it, if they have maintained sufficient links with that jurisdiction or have not displayed an intention to leave...

. Four states use the official title of commonwealth rather than state. State citizenship is flexible and no government approval is required to move between states

Freedom of movement

Freedom of movement, mobility rights or the right to travel is a human right concept that the constitutions of numerous states respect...

 (with the exception of convicts on parole

Parole

Parole may have different meanings depending on the field and judiciary system. All of the meanings originated from the French parole . Following its use in late-resurrected Anglo-French chivalric practice, the term became associated with the release of prisoners based on prisoners giving their...

).

The United States Constitution

United States Constitution

The Constitution of the United States is the supreme law of the United States of America. It is the framework for the organization of the United States government and for the relationship of the federal government with the states, citizens, and all people within the United States.The first three...

 allocates certain powers to the federal government.