Unlike "the Silk Road" or "the Middle Ages", "third world" was a term in contemporary use at the time it applies to, including among non-aligned states and NGOs that worked on third world cooperation.

It was pretty well-defined as political classifications go, and people involved in actual "entities" related to it were aware of and sometimes used the term.

When originally coined (circa 1950 around the Korean War), the First World was the US aligned block of countries, the Second World was the USSR aligned block of countries, and the Third World was all of the countries not part of either. Egypt, India, Yugoslavia, Ghana and Indonesia viewed themselves as leaders of the broader political movement during the 1960's and 1970's.

Even into the 1960's there were few industrialized nations outside of those two main blocks, so "Third World" quickly lost its explicitly political meaning and became more a description of the level of capital investment and worker productivity.