A jew, in a racist, discriminatory sense. According to
Wikipedia, the term "kike" was at first a discriminatory
word used by Jews who lived in Western Europe (France, UK or Germany) to refer to those who lived in Eastern Europe (
Poland, Romania or Russia), whose family names often ended with "ki". The term was later used by Christians and non-Jews against the whole Jewish population, so the term became a general ethnic slur against Jews in general.