Non-aligned countries didn't exist? Sorry I need some coffee and I'm feeling a little thick at the moment.
I always thought it was more about Developed/Developing/Undeveloped, mostly in terms of the industrial transition.
But, if we are being honest, it’s used a lot more as “third class”.
I suppose indeed that it is not really a well defined “thing”, like the Silk Road.
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.