State vs Nation
It is common for people and even leaders referring to their countries as nation or State. Though there is nothing wrong as a nation is often referred to as a member state frequently in world bodies such as UN, it has to be remembered that state and nations are treated as separate entities especially in political science. For one, when being referred to as a State, capital S is used instead of lowercase s to differentiate from ordinary word state that refers to condition of an object or entity. There are more differences in a State and a nation as described in this article.
A nation is a group of people who share common cultural heritage, a bonding because of shared history and geographical boundaries. People may or may not share same traditions, values, language, and religion. There are examples of nations that are multicultural and have people with different traditions and customs and even speak different languages. One great example of a nation that is a melting pot of languages is India that has unity in diversity. Even in such a country, there is a common thread of nationalism that binds the people together and makes the concept of a nation.
On the other hand, a state is defined as a patch of land with a sovereign government in political science. There are states that are also nations and in such circumstances they are called nation-states. The situation is troublesome when a state overlaps the boundaries of several nations and this is when there are often civil wars. At present there are 195 nations (including nation states). A state that is recognized as sovereign by outside countries is regarded as a nation.
There is another state (with a lower case s) which is one of the constituent parts of a country and nearly all countries of the world are divided into number of states. Some examples are the states of US and the states of India.