Refers to a person born to a Jewish Father and non-Jewish Mother. Due to the father's last name and/or inherited physical features such a person may be "seen" as "Jewish" by the majority non-Jewish culture while simulaneously being seen by the Jewish community as a non-Jew (or Goy) based on the matrilineal perspective of Jewish law. This term goy for a non-Jew may be seen as perjoritive whereas Gentile is the more respectful term. However given the disgust some have for intermarriage this term is often used to slur the offspring of such a relationship.
He looks Jewish but his Mother's maiden name is Smith...he must be a Jewgoy!