I lived in Argentina for a number of years, and Mexican was something of a mystery there as well. When I ordered a tortilla, I got and omelette. I hope this helps:
Tortilla: A thin, flat bread that can be made from wheat flour or corn flour (masa). The corn variety are cut up and fried, becoming tortilla chips or taco chips.
Tostada: A fried flat corn tortilla topped with a layer of beans, shredded beef or chicken, lettuce, tomatoes, cheese, avocado and salsa.
Taco: A corn tortilla folded over a filling.
Tamale: A corn husk stuffed with masa, meat or beans. Masa (dough) that surrounds your choice of filling, traditionally pork. The 5"-6" long and 1" thick tamale is wrapped in a soaked cornhusk and steamed to cook dough. Quesadilla: Grilled cheese sandwich made with a tortilla.
Flauta: Means "flute". Corn tortilla tightly rolled around a filling, then deep-fried.
Burrito/Burro: Large flour tortilla wrapped around a filling .
Chimichanga: Deep-fried meat-filled burritos.
Fajita: Skirt steak. Most people associate "fajita" with a taco or the strips of meat that go into the taco. Beef skirt steak comes from the outer covering of the breast near where the brisket comes from. There are only 2 skirts per cow, a highly flavorful cut of meat as a result of the fat membrane that ‘burns’ off when grilled. I use hanger steak, and that is what I am making tonight.
As far as I know, Tostito is just a brand name for tortilla chips.
Cheers,
Rob