The Second World is a term that was used during the Cold War to refer to the industrial socialist states that were under the influence of the Soviet Union. In the first two decades following World War II, 19 communist states emerged; all of these were at least originally within the Soviet sphere of influence, though some (notably, Yugoslavia and the People's Republic of China) broke with Moscow and developed their own path of socialism while retaining Communist governments. But most communist states remained part of this bloc until the fall of the Soviet Union in 1991; afterwards, only five Communist states remained: China, North Korea, Cuba, Laos, and Vietnam. Along with "First World" and "Third World", the term was used to divide the states of Earth into three broad categories.
The concept of "Second World" was a construct of the Cold War and the term is still largely used to describe former communist countries that are between poverty and prosperity, many of which are now capitalist states, such as Eastern Europe. Subsequently, the actual meaning of the terms "First World", "Second World" and "Third World" changed from being based on political ideology to an economic definition. The three-world theory has been criticized as crude and relatively outdated for its nominal ordering (1; 2; 3) and sociologists have instead used the words "developed", "developing", and "underdeveloped" as replacement terms for global stratification (which in turn have been criticized as displaying a colonialist mindset) --nevertheless, the three-world theory is still popular in contemporary literature and media. This might also cause semantic variation of the term between describing a region's political entities and its people.
The Three Worlds Model was used to rank the development of countries and their economies during the Cold War. First World countries were capitalist and industrial; they shared similar political and economic institutions, and retained influence over parts of the former colonial world. Second World countries advocated socialism and shared certain characteristics such as centrally planned economic systems, single- party states, and mainly medium income levels. The First World and the Second World were competing for political and economic influence over developing nations known as the Third World.
The Human Development Index is an index used to rank countries and is quantified by looking at a country's human development such as life expectancy, education, and per capita income indicators. The scale is 0-1 and they are put into one of 4 categories; 0-.55 is low, .55-.70 is medium, .70-.80 is high and very high tops out at .80-1.0. The Second World countries from the Cold War era currently range from medium human development to very high human development in terms of HDI.
Some examples of Second World countries are Bulgaria, Turkey, Hungary, Poland, Romania, Russia, and China. Second World countries are countries that are more stable and more developed than Third World countries which exist in parts of Africa, South and Central America and south Asia, but less stable and less developed than First World countries such as the United States. Developing countries are countries that are less industrialized and have a lower per capita income levels.
"Today I use the phrase to refer to those countries in Eastern Europe and Central Asia, Latin America, the middle east east and southeast Asia which is both rich and poor, developed and underdeveloped, Post modern in pre-modern, cosmopolitan and tribal - all of the same time." 
Today there are fewer dominant power centers in the world than was the case during most of history. Since World War II, smaller entities have joined what is now modern China and more than two dozen nation-states have integrated into the European Union. These two and the United States are the world's three natural empires. Some feel the Second World countries are the central stage on which the future course of global order is being determined.
The all-too-present weight of the Communist Party in China reminds us of the similarities to the Soviet Union (now Russia) during the Cold War. The notable differences are that the Soviet Union achieved growth under economic and political institutions because it forcibly allocated resources toward industry. In China the Communist Party controls the entire bureaucracy, armed forces, media and large parts of the economy.
second world countries communist.