federation (also known as a federal ) is a political entity characterized by a union of partially self-governing provinces, states, or other regions under a central federal  (federalism).

In a federation, the self-governing status of the component states, as well as the division of power between them and the central , is typically constitutionally entrenched and may not be altered by a unilateral decision of either party, the states or the federal political body.

Alternatively, a federation is a form of in which sovereign power is formally divided between a central authority and a number of constituent regions so that each retains some degree of control over its internal affairs.