Answer
The Einsatzgruppen were special task forces composed of Nazi German paramilitary units, including the Gestapo, the SS (Schutzstaffel), and the SD (Sicherheitsdienst or security service), that carried out mass killings during World War II, particularly in Eastern Europe. They played a central role in the Holocaust, targeting and murdering millions of Jews, as well as other minorities such as Roma, communists, and Soviet civilians.