Fajita is actually a cut of beef, the skirt steak, that was cheap and relatively good. The traditional preparation was to marinate overnight and then grill and slice very thin for tacos. Fajita has come to mean a taco, usually made with flour tortillas, filled with marinated grilled meat of any kind. A burrito is a tortilla roll, the filling can be almost anything, refried beans, beans, meat, lettuce, tomatoes, salsa, sour cream...etc. Burritos are made with flour tortillas as corn meal tortillas are too small and brittle. A taco is a tortilla that is simply folded over a filling of meat, refried beans, cheese...etc. The tortilla used to make a taco may be folded and deep fried (a crispy taco) or simply heated (a soft taco), flour tortillas are rarely used to make tacos.