Third World
The term "Third World" arose during the Cold War to define countries that remained non-aligned with either NATO or the Warsaw Pact. Canada, Japan, South Korea, Western European nations and their allies represented the First World, while the post-Soviet Union countries, China, Cuba, and their allies represented the Second World. This terminology provided a way of broadly categorizing the nations of the Earth into three groups based on political and economic divisions. Since the fall of the Soviet Union and the end of the Cold War, the term "Third World" has decreased in use. It is being replaced with terms such as developing countries, least developed countries or the Global South. The concept itself has become outdated as it no longer represents the current political or economic state of the world.
Eastern Bloc
The Eastern Bloc, also known as the Communist Bloc, the Socialist Bloc and the Soviet Bloc, was the group of communist states of Central and Eastern Europe, East Asia, and Southeast Asia under the hegemony of the Soviet Union (USSR) that existed during the Cold War (1947–1991) in opposition to the capitalist Western Bloc. In Western Europe, the term Eastern Bloc generally referred to the USSR and its satellite states in the Comecon (East Germany, Poland, Czechoslovakia, Hungary, Romania, Bulgaria, and Albania); in Asia, the Soviet Bloc comprised the Mongolian People's Republic, the Socialist Republic of Vietnam, the Lao People's Democratic Republic and the People's Republic of Kampuchea, the Democratic People's Republic of Korea, and the People's Republic of China (before the Sino-Soviet split in 1961). In the Americas, the Communist Bloc included the Caribbean Republic of Cuba since 1961 and Grenada.
Eastern Bloc
Soviet control of the Eastern Bloc was tested by the 1948 Czechoslovak coup d'état and the Tito–Stalin Split over the direction of the People's Federal Republic of Yugoslavia, the Chinese Communist Revolution (1949), and China's participation in the Korean War. After Stalin's death in 1953, the Korean War ceased with the 1954 Geneva Conference. In Europe, anti-Soviet sentiment provoked the Uprising of 1953 in East Germany. The break-up of the Eastern Bloc began in 1956 with Nikita Khrushchev's anti-Stalinist speech "On the Cult of Personality and Its Consequences". This speech was a factor in the Hungarian Revolution of 1956, which the Soviet Union suppressed. The Sino–Soviet split gave North Korea and North Vietnam more independence from both and facilitated the Soviet–Albanian split. The Cuban Missile Crisis preserved the Cuban Revolution from rollback by the United States, but Fidel Castro became increasingly independent of Soviet influence afterwards, most notably during the 1975 Cuban intervention in Angola. That year, the communist victory in former French Indochina following the end of the Vietnam War gave the Eastern Bloc renewed confidence after it had been frayed by Soviet leader Leonid Brezhnev's 1968 invasion of Czechoslovakia to suppress the Prague Spring. This led to the People's Republic of Albania withdrawing from the Warsaw Pact, briefly aligning with Mao Zedong's China until the Sino-Albanian split.

Question: "Third World" referred to countries that remained non-aligned with either NATO or a grouping of states aligned with who? 
Answer: Soviet Union