I remember visiting my best friend when she was studying Spanish in Merida, which is in the Yucatan peninsula of Mexico. She taught me the real difference between tacos, fajitas, burritos, enchiladas etc. A taco is simply meat or fish and toppings put inside a tortilla. You can use many different kinds of fish in a fish taco but my preference is monkfish because it is meaty yet has a light, delicate flavour.