A citizen is defined as a legal member of a state with full constitutional or legal rights in the country in which he or she resides. While an alien or a non-citizen is any individual who is not a national of a State in which he or she is present.

In general, price discrimination occurs when a producer sells a commodity to different buyers at different prices for reasons not associated with differences in cost. For example, doctors, lawyers and engineer sometimes vary their fees according to the incomes of their clients. Cinemas also charge lower admission prices for children.