The nationality of a person refers to the country in which he or she professes allegiance, with the country having some form of legal jurisdiction over that individual. Consequently, that person has a legal obligation to the laws of that state. It does not necessarily reflect the heritage of a person nor the country in which a person was born.
People can be born in a particular country, reside in a different country and have the latter country reflect their nationality. Simultaneously, a foreign national can reside in a different country and still profess allegiance to their former country. While nationality and citizenship are not overlapping, most citizens are, in fact, nationals, and nationals are citizens.