Why is the word "expat" a thing?

In theory, An expat is someone sent abroad on short/mid-term mission while working for an employer, while a migrant is someone moving abroad to find a job and sometimes to start a new life.

This means that, if let's say if a Mining company in Ghana sends someone to New-York to be the "US sales director" that person would be an an expat While an American opening an hotel in Ghana would be an immigrant.

But indeed, in many cases : Expat = European/North-American, Immigrant = From somewhere else

Because "immigrant bad" and they don't see themselves as bad.

A quick Google search says that an expat usually only lives in a new place for a limited period of time. An immigrant moves to a new place with intent to settle.

Whether that's how it's used colloquially is another matter...

Because immigrants are brown and poor.

I've always considered an expat to be different from immigrant in that it's temporary.

I lived abroad from 2009 to 2011, simply because I could, as my employer had to fly me in to work anyway - It didn't matter to me whether my home airport was TRD or PRG. I was chatting with someone local, and when I told them about my situation they're actually the ones who used the word expat. Personally I considered myself a long term tourist.

Why Brits and Americans? Every major city has expats.

You go abroad for a job, usually temporarily -> expat

You give up your citizenship to move to another country -> immigrant

Personally, I define an expat as someone living in another country and not learning the language/customs.

They will never be accepted as a local because of this.

The etymology might help break down some of the nuance here

According to etymonline the etymology for expatriate (often shortened to expat) is:

"to banish, send out of one's native country," 1768, modeled on French expatrier "banish" (14c.), from ex- "out of" (see ex-) + patrie "native land," from Latin patria "one's native country," from pater (genitive patris) "father" (see father (n.); also compare patriot). Related: Expatriated; expatriating. The noun is by 1818, "one who has been banished;" main modern sense of "one who chooses to live abroad" is by 1902.

Immigrate, is similar, but is more used to describe moving to a place:

"to pass into a place as a new inhabitant or resident," especially "to move to a country where one is not a native, for the purpose of settling permanently there," 1620s, from Latin immigratus, past participle of immigrare "to remove, go into, move in," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + migrare "to move" (see migration). Related: Immigrated; immigrating.

The closer synonym to expatriate would probably be emigrate, the opposite of immigrate, to leave a place.

As to why one might use expatriate over emigrate; consider the sentence "I'm an American immigrant". It's kind of unclear if you're trying to say that you are an American that has migrated to another country (as in "I'm an American immigrant living in Brussels"*), or someone who has migrated to America (as in "I'm an American immigrant from Slovakia"). Using expatriate removes the ambiguity: "I'm an American expatriate" and makes it clear that the speaker is trying to convey where they are from.

* technically, using emigrant here would be more clear, but English is a lawless and lazy language

I always assumed it was simply a matter of perspective. E.g. someone leaving the USA for the UK is an expat to the USA but an immigrant to the UK.

I've always interpreted it as someone who's here only temporarily. They plan to go back eventually and as such stick to expat social groups with similar issues for e. g. temp permits as opposed to permanent permits for immigrants.

cause usually its not permanent, like with immigrants.

It's not a British/American thing - any nationality can be referred to as an expat. It's all a matter of what you're trying to emphasize. The term "expat" implies being in a different country and feeling like a foreigner - using the term suggests that there is a degree of culture shock or not feeling like you fully fit in. Foreigners will often look for expat communities for support. That may be why you're noticing it with British and American foreigners - you can be a French expat or a German expat or any other nationality, but if English isn't your first language you're less likely to know the term.

You're also less likely to hear an American or British person refer to people who come to the U.S. or U.K. as "expats" - the term "expat"implies inclusivity with other people who came from the same place, while "immigrant" carries the implication of someone from a different culture that came here. As a native English speaker, I would think it sounds perfectly natural to hear someone say "I'm a Syrian expat", but I would only use the term to describe "the Syrian expat community" (i.e. the Syrians that have come here and are relying on each other for support). If I were describing the same person, I would say "Syrian immigrant" because I'm not the one feeling the culture shock of being in a foreign land. (or I would use the term "refugee" which carries the implication that they're here, but not by choice - they were forced out of their home)

"Immigrant" often also implies some sort of formal legal status, although in a looser sense it just means that you live in that country on a permanent basis. All immigrants are also expats, but not all expats are immigrants.

As others have pointed out here, while neither term is by itself positive or negative, "expat" will almost never be used in a negative sense, but "immigrant" can be used in a derogatory way, although it can also be neutral or positive depending on the speaker and context.

I hear the word expat all over the world, I don't think it's regional.

"immigrant" gives the impression that you are traveling to get to someplace, while expat implies that you are traveling to get away from someplace, as I've heard it used.

I call any non-native citizen (anyone not born in my country) an import.

Like beer.

Colloquially, expat tends to imply self funded, or at least bringing wealth with them in some respect. That's not what the word literally means but it's how I see it used. This is consistent even with foreign professionals coming to work in, say, London. Few people refer to them as immigrants though that's what they are technically. (I've seen people be called an "ex pat from their country" or an "international worker", these both in the city of London referring to office based professionals) The word immigrant seems to be reserved (at least in Britain) as a pejorative because it implies low skill and by further implication, a net cost on public services.

Because its a better word

There is another point, at least for Americans. While I know a few people who have emigrated to the US and still maintain ties with their original homeland, I know others who have intentionally given up their privileges back home. While they may still be citizens of their home country, they owe them no obligations.

The US is different, they tax your income no matter where in the world you make it. if you are living in a country with a tax treaty in the US, you can fully deduct all foreign tax payments so you will likely end up owing nothing to the US. But you still have to file. And in return for that you retain the right to vote from the state you last resided in. Furthermore, it is quite hard to give up your US citizenship. It can be very costly, because we will make you pay taxes on assets as if you sold them before they let you leave, including any retirement funds.

Americans living abroad are much more likely to still consider themselves Americans first, because we remind them about it every April 15th.