Any person other than a US citizen, US permanent or temporary legal resident alien, or person in US custody.
(1) an individual who is not a citizen of the United States or a national of the United States and has not been lawfully admitted to the U.S. for permanent residence, as defined in 8 U.S.C. §1101(a)(20); or (2) a foreign principal, as defined in 22 U.S.C. §611(b). 110.20(a)(3).
Foreign National has been defined 7 different ways in documents like Department of Defense Dictionary of Military and Associated Terms, Campaign Guide for Political Party Committees, Glossary For File Format For Levels Version 7.3, and 4 more.