I've decided to put this in writing. Too many times I overhear conversations at bars and restaurants on the difference between tacos, fajitas, and burritos. I'll admit, I didn't know the difference until my sophomore year in college when some co-workers and I got into a debate and consulted Wikipedia. So here is your educational post for the week. (Note: All info has been gleaned from the web so may not be 100% accurate, but I trust it for this.)
First, we are going to define taco, According to Wikipedia
So basically anything that is put inside of a corn or wheat tortilla and folded up prior to eating can be called a taco.
Next Wikipedia define's burrito for us.
This is an awful definition so let's go to the wonderful world of the web. via Dictionary.com
1940–45; < MexSp (Guerrero): stuffed taco, Sp: young donkey, foal, equiv. to burr(o) burro + -ito dim. suffix
From what I can gather the difference between a taco and a burrito has nothing to do with fillings but how it's folded. Basically a taco is not enclosed and burrito is folded in a while to fully enclose the fillings on all sides prior to eating.
Next to tackle the food that started it all. I tweeted this earlier and then realized I was mistaken.
Fajita as defined by Wikipedia
So a fajita is the same as a taco, but originally it was only supposed to refer to a taco filled with skirt steak. As the word evolved it changed. Once again, via Wikipedia.
Regardless, use of the word fajita has evolved from the term for a cut of beef to include the cooking method (thus chicken fajita) and also to define the grilled strips of peppers and onions that usually accompany the meat.
So here is my uneducated opinion. Tacos are served in a folded or rolled tortilla that is open on both ends. Burritos are served in a tortilla that has been completly sealed. Fajitas are tortillas filled with grilled meat and are served with peppers and onions.
Does anyone want to correct me?