A "foreign national" is any person who is not a US Citizen:

"The United States Department of State defines a “foreign national” as anyone who is not a “U.S. person.” A “U.S. person” is any one of the following: U.S. citizen; Lawful permanent resident (green card holder); and “Protected Person” i.e. political asylum holder." [0]

A foreign national is a person or organization who is not a citizen of the United States, and who is a citizen of a foreign country. The Immigration and Nationality Act (INA) uses the term "alien" to refer to a person who is not a United States citizen, and does not use the term "foreign national."[1]

[0] https://www.orc.msstate.edu/faq/what-department-states-defin...

[1] https://www.law.cornell.edu/wex/foreign_national

I also found this: https://www.uscis.gov/tools/glossary

    > Foreign national: A person without U.S. citizenship or nationality (may include a stateless person). This term is synonymous with “alien”