[usrusr]

That's the difference, and it is inevitably an international one (e.g. we happily adopted the English term "expat" here in Germany) because it only exists across borders. But the difference gets muddied a lot because one is associated with much higher status than the other and everybody will naturally try for the higher status label if there is the remote chance of getting away with it.

Higher status? "People who hang out with diplomats", try beating that. If you routinely dine at your embassy you'd sure be considered "expat" even if you are from Afghanistan. Of course only a tiny fraction of expats would actually do this, but it illustrates the idea. A more practical line of distinction: would they seems their children to regular local schools? If they insist on private "international schools", then it's "expat", otherwise only if a return date is known.