It was a term coined in the West and used by both sides to identify which set of nations were were pro-Soviet. It's opposite was the Western bloc/the West. It consisted of the USSR, Bulgaria, Romania, East Germany, Czechoslovakia, Poland and Hungary. Albania left in 1960 and Yugoslavia got kicked out in the late 1940s. Mongolia, Vietnam, S. Yemen, Afghanistan, Nicaragua, North Korea, Egypt and Cuba have been included in the wider use of term on some occasions to. The Eastern bloc was politically Communist and/or Socialist.