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.