Commonwealths
Four of the states bear the formal title of commonwealth: Kentucky, Massachusetts, Pennsylvania, and Virginia. This is merely a legacy of all four states' history, and their formal name has no effect on their legal status as states.
Somewhat confusingly, the U.S. territories of the Northern Marianas and Puerto Rico are also referred to as commonwealths, and that designation does have a legal status different from that of the 50 states. Both of these commonwealths are unincorporated territories of the United States.
Read more about this topic: U.S. State