It is time to dump the phrase 'developing world'. 'Developing' is a misnomer, given that many countries are not developing at all, but remaining economically static. A few are falling backwards. The previous phrase 'third world' is also pretty useless, since the 'second' (communist) world imploded.
I propose a new terminology: globalised, globalising and non-globalised. I recognise that there are many countries that would be difficult to classify - but that is a problem with all such terminology.
The 'globalised world' refers to successful capitalist economies, engaged with international trade.
The 'globalising world' refers to those less successful economies, which are nonetheless engaged with globalisation and developing fast. Not all are fully capitalist - China being a notable example. This is often why the countries are backward in the first place.
The 'non-globalised world' refers to countries like Zimbabwe and Cuba, which are not developing. It would also include failed states such as Sudan and Haiti.
While leftists like to pretend that globalisation means that the rich are getting richer and the poor are getting poorer, the facts are quite different. Rich countries are indeed getting richer, but those poor countries which are engaged with globalisation are also getting richer. Indeed, they are mostly growing much faster, though of course from a lower base. In other words, they are closing the gap.
The advantage of this terminology is that it recognises the key difference between those countries which are developing and those which are not. Far more people live in these rapidly developing countries than in the basket-case countries that are flatlining or falling backwards. Indeed, just three globalising countries - China, India, and Indonesia - have 40% of the world's population, and these countries are developing very rapidly.