A foreign national is any person who is not a national of a particular country.
The law of Canada divides people into three major groups: citizens, permanent residents, and foreign nationals.
Under Section 2 of the Immigration and Refugee Protection of Canada (IRPA), "foreign national means a person who is not a Canadian citizen or a permanent resident, and includes a stateless person."
The term foreign national is not defined in US immigration law, which uses the term alien instead.
However, the term is used in US election law to identify people who are not allowed to contribute to federal campaigns.
For that purpose, the definition excludes permanent residents even though they do not possess US nationality: "the term 'foreign national' means... an individual who is not a citizen of the United States or a national of the United States (as defined in section of title 8) and who is not lawfully admitted for permanent residence, as defined by section of title 8."
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Foreign national.