The Nazis categorised the identities of the population by introducing laws. The identities they gave people were based on the following concepts, some of which overlap:
Ethnicity or Race - Romani / Sinti (Gypsy), Aryan, Jew, Black, Slav
Religion - Jehovah Witnesses, Jew
Sexuality - Homosexual [Gay]
Politics - Communist, Socialist, Democrat
It became clear in Nazi Germany that if you had the legal papers to show you were a German national then you had rights denied to others.