A foreign national is defined simply as “an individual who is a citizen of any country other than the United States.
Nonresident Aliens vs. Resident Aliens for Tax Purposes
Immigration terminology and definitions are not the same as tax terminology and definitions, therefore a nonresident alien for tax purposes is different than a nonresident alien for immigration purposes. A foreign national must be correctly classified in order to avoid potentially serious problems including:
Comparison of Nonresident Alien vs. Resident Alien for Tax Purposes