Looking at online dictionaries there is no hint of temporariness [0], [1]. Wikipedia refers to it as "a person who resides outside their native country" and often referring to "a professional, skilled worker or artist from a wealthy country" [2], which matches exactly the way I see it used. Similar to other commenters here, I also mostly encounter it being used by skilled, first world professionals to separate themselves "from the plebs" of poorer immigrants.
replyPS I do not disagree that some use cases could include temporariness (wikipedia mentions academic discourse and something about some british civil workers a few decades ago) but this is by far neither the unique nor the most common way it is used nowadays, nor how historically it has often been used long before.
[0] https://dictionary.cambridge.org/us/dictionary/english/expat...