“Global South” is the currently used term for what was previously called “Developing Countries” and “Third World Countries” before that.
The global south is not equal to the geographical south, otherwise they could’ve just said the southern hemisphere.
According to Wikipedia[1], Australia is considered part of the “Global North”. It’s an economic label more than a geographic one.
[1] https://en.wikipedia.org/wiki/Global_North_and_Global_South