What is the formal definition of expatriate?

A person who is currently living and well established in a foreign country but will be hired by another foreign country is considered an expatriate?

The laws of some countries enforce some benefits for an expatriate, but even if one is not formally considered an expatriate, which benefits can one reasonably expect from the company? For instance, what kind of expenses is usually required and for how long should these expenses be paid by the company?

Thank you for any advice.