Third World countries (now known as “developing nations”) are countries with a low “Human Development Index.” First World countries (like the United States, Japan, and Germany) score much higher on the HDI. A nation’s HDI is determined by its literacy rate, poverty rate, life expectancy, etc.There is indeed a Second World, though the expression isn’t exactly parallel to the other terms, and these days, few mention it. According to Nations Online, the phrase refers to “former communist-socialist, industrial states, the territory and sphere of influence of the Union of Soviet Socialists Republic.” For example, Romania, Hungary, Latvia, and of course, the big bear — Mother Russia. China is also considered a Second World nation.
Thanks to the fall of the Soviet Union, the term “Second World” has become rather meaningless. Nowadays, a country’s economic strength (not its government) determines how it’s classified. Countries in Europe and North America as well as Australia are primarily First World, while Africa and South America are mostly made up of developing nations. Hopefully with economic aid and other support, the gap between the haves and the have-nots will grow smaller, and the need for words to distinguish them will disappear.