The first term used to describe India is sovereign. What does it mean? It means supremacy of power that is not limited by any law inside or outside the state. Sovereignty is a basic characteristic of the state. A state cannot exist unless it is sovereign. There are four basic characteristics of the state: People, government, territory, and sovereignty. Out of these four, sovereignty is the most important one, because it distinguishes a state from other forms of human institutions. Other institutions may have people, they may have government and administration of their own, they may possess land, but unless they have sovereignty, they cannot be termed as states. For example, Indian Cricket Board has people, autonomous administration, they possess their land, but it is not state because it is responsible to some another authority. It has to follow the laws of India. Similarly, the states of Maharashtra, Kerla, or any other state, they have three other components but do not have sovereignty, so they are not states in a legal perspective.
In the preamble, we have proclaimed our sovereignty in ourselves. In a democratic country like ours, people are sovereign. This is called as popular sovereignty. But legally, our sovereignty lies in our constitution and the authorities described by it.