A state is a constituent political entity of the United States. There are currently 50 states, which are bound together in a union with each other. Each state holds governmental jurisdiction over a defined geographic territory and shares its sovereignty with the United States federal government. Due to the shared sovereignty between each state and the federal government, Americans are citizens of both the federal republic and of the state in which they reside. State citizenship and residency are flexible, and no government approval is required to move between states, except for persons restricted by certain types of court orders. Four states use the term commonwealth rather than state in their full official names.