Generalplan Ost (GPO) (English: Master Plan East) was a secret Nazi German plan for the colonization of Central and Eastern Europe). Implementing it would have necessitated genocide and ethnic cleansing on a vast scale to be undertaken in the these European territories occupied by Germany during World War II. It would have included the extermination of most Slavic people in Europe. The plan, prepared in the years 1939-1942, was part of Adolf Hitler's and the Nazi movement's Lebensraum policy and a fulfilment of the Drang nach Osten (English: Drive towards the East) ideology of German expansion to the east, both of them part of the larger plan to establish the New Order.
Read more about Generalplan Ost: Development and Reconstruction of The Plan, Phases of The Plan and Its Implementation, Civilian Death Toll in The Soviet Union