The Katyn massacre (Polish: zbrodnia katyńska, mord katyński, "Katyń crime"; Russian: Катынский расстрел Katynskij ra'sstrel, "Katyn shooting") was a series of mass executions of Polish nationals carried out by the People's Commissariat for Internal Affairs (NKVD), the Soviet secret police, in April and May 1940. Originally the term "Katyn massacre", also known as the Katyn Forest massacre, referred to the massacre at Katyn Forest, which was discovered first and was the largest execution of this type.