[graemep]

That is the original definition, but then all immigrants are expats, and all expats are migrants. The words become synonyms. Then its become very interesting to ask why people prefer one word over the other for particular groups of people.

[ralferoo]

To me, it's useful because it frames it in terms of social connections in the target country and because how it works with an adjective.

So, British expats in Spain and Chinese expats in Spain are likely to socialise in their specific group, but rarely if ever intersect. They are all immigrants in the target country (and especially when considered as a whole as everyone from "outside"), and they are all expats (but probably in defined cliques).

I'd say these clusters of people are living the "expat life", but equally there are many immigrants who don't particularly want to hang out with other expats, because they're not trying to recreate where they left in a new place, but are trying to assimilate to the new place. They themselves are still expats even if they don't socialise much with other expats, but wouldn't be living the expat life.