Use of the term "Eastern Bloc" generally refers to the states forming the Warsaw Pact. Some define it simply as "communist states of eastern Europe." Sometimes, more generally, they are referred to as "the countries of Eastern Europe under communism".
Even though Yugoslavia was a socialist country, it was not a member of COMECON or the Warsaw Pact. Parting with the USSR in 1948, Yugoslavia did not belong to the East, but also did not belong to the West, because of its socialist system and its status as a founding member of the Non-Aligned Movement. However, many sources consider Yugoslavia to be a member of the Eastern Bloc. Others consider Yugoslavia not to be a member after it broke with Soviet policy in the 1948 Tito–Stalin split.
The term "Eastern Bloc" was sometimes used interchangeably with the term Second World, being considered one of the two main blocs of the Cold War, opposed by the Western Bloc. The Soviet-aligned members of the Eastern Bloc besides the Soviet Union are often referred to as "satellite states" of the Soviet Union.
Prior to this use of the term, in the 1920s, "Eastern bloc" was used to refer to a loose alliance of eastern and central European countries.
Other countries that were not Soviet Socialist Republics, not Soviet Satellite States or not in Europe were sometimes referred to as being part of the Eastern Bloc, Soviet Bloc, or Communist Bloc, including: