A foreign national is a person who is visiting or living in a country where they are not a citizen.
The European Union has a different definition of "foreign national." In the European Union, a person is only thought of as a foreign national if they are not a citizen of any country in the European Union. These people are called "third party nationals," not "foreign nationals."
The United States Department of Homeland Security says that a foreign national as a person "who is a citizen of any country other than the United States."
In other words, a foreign national is a person who: