Refers to a person who is a native or citizen of a particular country, often used in contrast to foreigners or immigrants.
He asserted his rights as a native citizen.
In that country, treatment differs between natives and foreigners.
外国人 means 'foreigner', the direct opposite of 本国人.
Compound of 本国 (home country) + 人 (person). The exact historical derivation is uncertain, but the word follows a common pattern for forming nationality terms.