Regarding the definition, they use the one Wikipedia mentions [1], namely, "the Global North consists of the world's developed countries, whereas the Global South consists of the world's developing countries and least developed countries". So the answer to "who comes up with this" would be "the United Nations Conference on Trade and Development". Both China and India are considered Global South.
[1] https://en.wikipedia.org/wiki/Global_North_and_Global_South