commonwealth defined

Kentucky is one of four American states designated as a commonwealth; Pennsylvania, Virginia, and Massachusetts being the other three. 

What does that mean exactly?

The English noun commonwealth dates from the fifteenth century. The original phrase "common wealth" or "the common weal" comes from the old meaning of "wealth" which is "well-being". The term literally meant "common well-being". ...cite

In the terminology of the United States insular areas, a Commonwealth is a type of organized but unincorporated dependent territory. ...cite

A form of government, named for the concept that everything that is not owned by specific individuals or groups is owned collectively by everyone in the governmental unit, as opposed to a state, where the state itself owns such things; Approximately, a republic ...cite