A nation is a form of cultural or social community. Nationhood is an ethical and philosophical doctrine and is the starting point for the ideology of nationalism. Members of a "nation" share a common identity, and usually a common origin, in the sense of history, ancestry, parentage or descent. A nation extends across generations, and includes the dead as full members. Past events are framed in this context; for example; by referring to "our soldiers" in conflicts which took place hundreds of years ago. More vaguely, nations are assumed to include future generations.A nation is usually the people of a state, and while traditionally monocultural, it may also be multicultural in its self-definition. The term nation is often used as a synonym for ethnic group (sometimes "ethnos"), but although ethnicity is now one of the most important aspects of cultural or social identity, people with the same ethnic origin may live in different nation-states and be treated as members of separate nation
Source:
http://en.wikipedia.org/wiki/Nation