who is an EXPAT?

I have decided that to start this new BLOG dedicated to expats and expats' life I shall first of all give a definition of what or better who is an expat, which kind of criteria are used to define someone as an expat. From tresaurus dictionary an expat (short for expatriate) is ''a person who is voluntarily absent from home or country''
....and what is the difference between expat and emigrant? and again what kind of meaning shall we give to ''voluntarily''? I will look into all the different aspects that create a person an expat, the benefits and difficulties that being away from home country can mean.

If interested and have topics and questions to ask me please write your comment and I will be happy to write about them.