Xenophobia is the hatred/contempt or fear (but usually hatred, the way we mean it) of outsiders. What particular kind of outsiders is up to the individual xenophobe, but it is most often used to refer to foreigners or to minority group strongly associated with a foreign country deemed threatening. However, for a particularly provincial person, it could also refer to people from outside the particular state/province, county, or town.
Few people will ever admit to being xenophobic, instead trying to pretend that it is some particular, justified concern that makes them want to keep all foreigners away.
Not to be confused with the fear of the TV show Xena: Warrior Princess or its title character.