Federation is a form of government in which sovereign power is formally divided between a central authority and a number of constituent regions so that each region retains some degree of control of its internal affairs.The governmental or constitutional structure found in a federation is known as federalism. It can be considered the opposite of another system, the unitary state. Germany, with sixteen Bundesländer, is an example of a federation, whereas neighboring Austria and its Bundesländer was a unitary state with administrative divisions that became federated, and neighboring France by contrast has always been unitary.
A unitary state is a state governed as one single power in which the central government is ultimately supreme and any administrative divisions (subnational units) exercise only powers that their central government chooses to delegate. The majority of states in the world have a unitary system of government.
India is considered as a Union of States because our Constitution allocates powers to both center and states with more powers to the center. Article 1 of the Constitution describes India as a “Union of States.” This means, India is a union comprising of various States which are integral parts of it.Union of States implies that “Indian federation is not the result of an agreement by the states” and “No state has right to secede from the federation”. Federalism means allocation of powers between the Center and States.The definition of a federation is the act of joining states or other groups with an agreement they will be governed under one central authority.Federation (also known as a federal state) is a political entity characterized by a union of partially self-governing states or regions under a central (federal) government.Federal power means power is divided between a central authority and its constituent political units(can be considered as states).