In political science, a "nation" refers to a group of people who feel bound into a single body by shared culture, values, folkways, religion and/or language.  A "state" just refers to a patch of land with a sovereign government.  States often coincide with nations (and are called "nation-states," but not always.  States that overlap multiple nations tend to have civil wars; states that exclude parts of a nation tend to have wars with the neighboring state(s) that contain the rest of the nation.
What is the difference between a state and a nation?