Short answers, pulled from the story.
Alfred Sauvy, a French demographer, anthropologist, and historian, coined the term "third world" (tiers monde) in an article published in the French magazine L'Observateur on the 14th of August, 1952. He drew the phrase from the Third Estate of pre-revolutionary France. The concept may have been in circulation even earlier, at the 1947 Asian Relations Conference in New Delhi.
Third World was originally a political term designating countries that remained non-aligned with either NATO (the First World) or the Warsaw Pact (the Second World). It was not primarily an economic classification; the association with poverty and underdevelopment came later as a stereotype, because many non-aligned nations happened to be economically poor and non-industrialized.
Mao Zedong's Three Worlds Theory, articulated in the early 1970s and pronounced at the UN General Assembly in 1974 by Deng Xiaoping, grouped the United States and the Soviet Union together as the First World because Mao viewed both as hegemonic superpowers. In the Western framework China was Second World and India was Third World, but in Mao's framework both China and India were part of the Third World, defined as exploited nations.
Peter Bauer argued in the 1980s that Third World status was assigned by no stable economic or political criteria and was largely arbitrary. The only characteristic he found common to all Third World countries was that their governments demanded and received Western aid, a system he strongly opposed. He considered the aggregate term misleading because the countries it grouped together had no consistent or collective identity.
Third-worldism is a political movement advocating unity among third-world nations against first-world influence and the principle of non-interference in other countries' domestic affairs. Its most notable institutional representatives are the Non-Aligned Movement and the Group of 77, which provide platforms for diplomacy among third-world countries and between them and the first and second worlds. Critics have accused the movement of providing cover for human rights violations by dictatorships.
Since the dissolution of the Soviet Union, terms such as developing countries, least developed countries, and the Global South have been widely used in place of Third World. Around the early 1960s the phrase "underdeveloped countries" was common, which was later replaced by "developing" and "less-developed" countries as politicians found earlier terminology contributed to stereotypes.