Four of the constituent states of the United States officially designate themselves Commonwealths: Kentucky, Massachusetts, Pennsylvania, and Virginia. This designation, which has no constitutional impact, emphasizes that they have a “government based on the common consent of the people” as opposed to one legitimized through their earlier Royal Colony status. People do not make the distinction between state or commonwealth. The four US states, which call themselves Commonwealth, can be referred to as state, too. It is a synonym.

There is no difference between a commonwealth and a state in the U.S. To Locke, Hobbes, and other 17th-century writers the term “commonwealth” meant an organized political community — what we today call a “state.” Officially Pennsylvania, Kentucky, Virginia, and Massachusetts are all commonwealths. When Pennsylvania, Kentucky, Virginia, and Massachusetts became part of the United States, they merely took the old form of state in their title.

…I know this is kinda confusing.

Today the term is more general and means a political community.

The type of community indicated by the term commonwealth varies. For instance, in different contexts it might indicate:

a political unit founded in law by agreement of the people for the common good;

a federated union of constituent states;

a community of sovereign states;

a republic;

a democratic constitutional monarchy;

When capitalised, “Commonwealth” normally refers to the 53 member Commonwealth of Nations—formerly the “British Commonwealth”—a loose confederation of nations formerly members of the British Empire (with one exception: Mozambique, which was a Portuguese possession). The Commonwealth’s membership includes both republics and monarchies and the (appointed, not hereditary) head of the Commonwealth of Nations is Queen Elizabeth II. She also reigns as monarch directly in a number of states, known as Commonwealth Realms, notably the United Kingdom, Australia, Canada, and New Zealand. The Commonwealth of Nations is sometimes referred as the New Commonwealth in a British context.

The Commonwealth of Independent States (CIS) is a loose alliance or confederation consisting of 12 of the 15 former Soviet Republics. Its creation signaled the dissolution of the Soviet Union, its purpose being to “allow a civilized divorce” between the Soviet Republics. The CIS has developed as a forum by which the member-states can co-operate in economics, defense and foreign policy.

A state is a political association with effective dominion over a geographic area. It usually includes the set of institutions that claim the authority to make the rules that govern the people of the society in that territory, though its status as a state often depends in part on being recognized by a number of other states as having internal and external sovereignty over it. In sociology, the state is normally identified with these institutions: in Max Weber’s influential definition, it is that organization that has a “monopoly on the legitimate use of physical force within a given territory,” which may include the armed forces, civil service or state bureaucracy, courts, and police.

A state is a politically organized body of people occupying a definite territory.