The literal definition is 'North American', applying to residents of all of the countries of North America. However, typically it's used as a more politically correct way of saying 'from the United States' because in Spanish America does in fact refer to two continents comprising of 35 countries, not just one. Central and South Americans might take exception to the usage of 'americano' because it insinuates that they are not Americans as well.
Gringo: Soy americano.
Tico: No, nosotros somos americanos--usted es norteamericano.