Nation is a population having a common language and literature, a common tradition and history, common customs, and a common consciousness of rights and wrongs, inhabiting a territory of a geographic unity. A society of men is said to constitute a nation when they feel conscious of their common racial or cultural or sentimental solidarity among themselves. In sum, a nation exists where its component atoms believe it to be a nation.
What are then the differences between nation and state? Nation is an ethnical concept while state is a political or legal concept. A state presupposes a government and a definite territory, while these are not necessary for a nation to exist. There can be a nation without there being a state, but where there is a state, there is at least one nation. A state may be made up of one or more nations, it is called a poly-national state. But where there is only one nation in one state, it is called a mono-national state.