Xenophobia is a dislike and/or fear of that which is unknown or different from oneself. It comes from the Greek words ξένος (xenos), meaning "stranger," "foreigner" and φόβος (phobos), meaning "fear." The term is typically used to describe a fear or dislike of foreigners or of people significantly different from oneself, usually in the context of visibly differentiated minorities.
A political poster of the far right National Democratic Party of Germany. The text reads, "We clean up."
According to the Oxford English Dictionary (OED), the word xenophobia consists of two parts: xeno (a combining form meaning "guest, stranger, person that looks different, foreigner") and phobia, ("fear, horror or aversion, especially if morbid").
It is more broadly defined in the Dictionary of Psychology "a fear of strangers".  As defined by the OED, it can mean a fear of or aversion to, not only persons from other countries, but other cultures, subcultures and subsets of belief systems; in short, anyone who meets any list of criteria about their origin, religion, personal beliefs, habits, language, orientations, or any other criteria. While some will state that the "target" group is a set of persons not accepted by the society, in reality only the phobic person need hold the belief that the target group is not (or should not be) accepted by society. While the phobic person is aware of the aversion (even hatred) of the target group, they may not identify it or accept it as a fear.
As with all phobias, a xenophobic person has to genuinely think or believe at some level that the target is in fact a foreigner. This arguably separates xenophobia from racism and ordinary prejudice in that someone of a different race does not necessarily have to be of a different nationality. In various contexts, the terms "xenophobia" and "racism" seem to be used interchangeably, though they can have wholly different meanings (xenophobia can be based on various aspects, racism being based solely on race and ancestry).
Xenophobia has two main objects:
The first is a population group present within a society that is not considered part of that society. Often they are recent immigrants, but xenophobia may be directed against a group which has been present for centuries, or became part of this society through conquest and territorial expansion. This form of xenophobia can elicit or facilitate hostile and violent reactions, such as mass expulsion of immigrants, pogroms or in the worst case, genocide.
The second form of xenophobia is primarily cultural, and the objects of the phobia are cultural elements which are considered alien. All cultures are subject to external influences, but cultural xenophobia is often narrowly directed, for instance, at foreign loan words in a national language. It rarely leads to aggression against individual persons, but can result in political campaigns for cultural or linguistic purification. Isolationism, a general aversion of foreign affairs, is not accurately described as xenophobia.
Racism by country
1. Oxford English
Dictionary' (OED). Oxford Press, 1971, eighteenth printing 1979.