What is the meaning of ‘national’ as in eg ‘Australian national’?

From here: https://academia.stackexchange.com/questions/115930/career-prospects-for-a-math-phd-student-in-pure-math

from a user who has also asked questions here: Where should I get travel insurance for a Chinese student in Australia travelling to the USA and then travelling to China?

I am an Australian national and want to live in Australia long term.

what exactly is the meaning of Australian national? like student visa? or actual citizen? or resident?