There's two different definitions. The common terminology for impoverished and/or undeveloped countries, whereas the above is the more legal terminology and original definition.
Well, technically, the term the meme is describing is The Non-Aligned Movement. The movement started in 1955 as a way for those countries not siding with the US or the USSR to create policy.
Merriam Webster:
1 :a group of nations especially in Africa and Asia not aligned with either the Communist or the non-Communist blocs
2 :an aggregate of minority groups within a larger predominant culture
3 :the aggregate of the underdeveloped nations of the world
emm... cuba.. .-. it was by far one of the most aligned to the communist block country and it is, indeed, a third world country.. so the term DOES connote a poor country.
1 :a group of nations especially in Africa and Asia not aligned with either the Communist or the non-Communist blocs
2 :an aggregate of minority groups within a larger predominant culture
3 :the aggregate of the underdeveloped nations of the world