I don't know if it is a perfect term, but it doesn't literally refer to any specific "South", rather I think it is a reference to the coincidence that many of the heavily industrialized empires of the 18th, 19th and 20th centuries have been in the northern hemisphere, and the general colonial power dynamic therein set up has lead to the term "Global South" meaning pretty much anywhere that has gotten the short end of the colonialism stick, vs the long end.

https://en.m.wikipedia.org/wiki/Global_North_and_Global_South