If you have been on this site, or the rest of the internet, for any length of time, you will be quite familiar with the notion of Australia being a seemingly alien place. From kangaroos to giant, murderous bugs, from tacking a bed onto the back of a sedan to celebrating winning a race with one by drinking beer from your shoe.
But few are aware of that reputation's role in fanfiction.
You see, back before the search engine went from a tool to assist with car repair -hence its name- to a portal to infinite sources of quality information about anything (this blog included!), research was cumbersome and time-consuming, and relied on someone having thought the information worth putting in a book. So authors that sought to write about stories set in a foreign land would see their comfort fic turn into a discomfort fic after yet another day spent at the library trying to work out how much the coffee shop would charge.
Thus, it quickly became praxis to sidestep the issue by setting the story in the writer's homeland, which they could confidently write about... or in a country no one else would know enough about to call out mistakes either. And Australia, of course, was a very popular pick, not just because it was safe to bank on none of your readers having been there, but because it was a context so far removed as to allow a degree of creative freedom - whatever form of government structure, social gathering, building code etcetera was most convenient or fun for your story, you could just pretend it was a thing in Australia!
Of course, the wild differences between the various, completely inconsistent Australias fic readers would encounter immediately made this trick a bit of a laughing stock, and as time went on, it became adopted in an increasingly ironic form, ultimately leading to authors jokingly referring to a setting they'd completely made up as "their Australia". That wording is, of course, still in use today, though with time it has been shorthanded through Australia's country code, AU.