Definitions
a foreigner = a person from a country other than one's own
an outsider = a person who is not (or is not accepted as) a member of a group or society. e.g. "Although she has lived here for ten years, the villagers still treat her as an outsider."
a stranger = 1. A person that one does not know
2. A person in a new or unfamiliar place or with people that he does not know