Though there are many theories on the origin of the word "Gringo", none have been proven. Regardless of the origin, a Gringo is anyone hailing from the United States (Canada is not included). Expats is short for "Expatriots" - people who are citizens of one country but are residing in another. I'm a Gringo Expat.
A friend of mine sent me an email the other day that I thought was both funny and accurate. I'll quote directly:
"...if you’re in Costa Rica it’s because you’re wanted or your unwanted. Gringos in Costa Rica fall into five distinct categories:
1. Running a scam.
2. Failed at whatever business they were in in the U.S. (e.g. real estate sales) and think they have a better shot at it in the tropics.
3. Here for the legal chicas because they can’t get them back home.
4. Here for the illegal chicas (or chicos) because they’re less likely to be caught on camera by Dateline reporters here.
5. Settled down with one chica and working in a legitimate job."
I would say, based on my experience, that these categories are listed in order of prevalence. Thankfully, and by no accident, my friend and I both fall into category 5.