What is third wold

There are basically 4 groups of nations in the world. First and second world are old
industrialized nations of the world, first world usually includes Italy, Britain ,and as such
which are like the old bunch of the block, then second world are the countries like USA, Japan,
western Europe, however because of similarity between industrialization and development of
the nations of first and second world, they are interchangeable and just called first world
collectively, third world are actually two groups of nations one who are growing super fast like
Hong Kong, Thailand, Malaysia and others second group is of china and India which are
growing moderately. and fourth world is of nations which are not growing at all like in Africa .
They have no resources to base their development on.
this is the economic real defination of it.

if you want a dictionary type political definition of it then

United States and its allies. Soviet Union and its allies. Third World: Non-alignedand neutral countries