There is a difference, and it has to do with how the US government treats you. I am an expat, living in the Caribbean. I list my US citizenship first, travel on a US passport, and pay US taxes. (Yes, even on money earned out of country, over a certain level.) My husband, on the other hand, renounced his US citizenship, no longer has a US passport, and will not pay them taxes after this year. He is an immigrant.