Basically, what Kaz said. An expatriate is someone living in a country other than the one in which they hold their primary citizenship.

It sounds like what you're asking about is expat packages in the workplace vs. being "on the local payroll."

>>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?<<

The laws of some countries allow employers to keep foreign workers out of the local social insurances regimes - if the foreigners are only going to be in the country for a limited amount of time (say, up to 5 years or so). It is assumed that the foreign workers will, during this time, be maintaining their eligibility in their home social benefits plans. For example, here in France, an American working for an international or US company can stay out of the French social system for 5 years, though during this time they must continue to pay into US Social Security and the US based employer health insurance plan. They still have to pay French income taxes while they are resident here.

It's entirely up to the employers what benefits accrue to those considered to be on "expat packages" rather than just being a foreigner hired onto the local payroll. These usually include things like: moving expenses covered, international school for the kids, a company car or car allowance, housing costs paid (especially if the expat has a house in their home country to which they will return at the end of the assignment), tax preparation assistance and tax equalization (especially for American expats, who continue to have to file returns even while resident abroad), a special "relocation bonus" to cover replacement of household goods or electrical appliances in the new location, once a year home leave, etc.

But to my knowledge, there are no laws governing what expatriate perks an employer has to offer. It's pretty much "whatever it takes" to convince the employee to accept the overseas assignment. Obviously, it's in the employer's interest to minimize the time they pay out for these perks, and they may be very keen to move an expat employee onto the local payroll as soon as it is determined that the person is not interested in returning home.

As far as the host country is concerned, a foreigner is a foreigner (and is usually taking a job that "should" be going to a local). The employer must obey the local labor laws (minimum wages, paying people on time, withholding any social charges or taxes that are required, etc.) and is usually responsible for making sure the foreigner is "street legal" (i.e. has work privileges) before hiring them or bringing them over to work. Past that, "you're on your own."
Cheers,
Bev