The "Iron Curtain" was the western boundary of the Soviet satellite nations in Europe.
The nations in Eastern Europe that aligned with the communist stance of the Soviet Union were also referred to as the Eastern Bloc, whereas the democratic nations of Western Europe were known as the Western Bloc.
British prime minister Winston Churchill is the person who coined the term "Iron Curtain," in a speech he gave in 1946. Churchill said that the nations which fell behind that boundary existed in what he called "the Soviet sphere" and were at least under the influence of the USSR if not, in fact, direct control from Moscow.