Ex patriots move to work in a foreign country for a limited period, with the intention of returning to their home country. Typically these are white collar workers who move between their employer's offices for 2-3 years and then return home.

Immigrants move with the intention of staying in the new country long term.

However, with the negative connotations attached to immigrants, some people - primarily white, highly educated people - incorrectly refer to themselves as expats, even once it's clear they intend to stay.