It's almost always...
...A
tortilla with meat, cheese and lettuce.
No, seriously.
What is a taco? A tortilla with meat, cheese and lettuce.
What is a burrtio? A tortilla with meat, cheese and lettuce.
What is a
fajita? A tortilla with meat, cheese and lettuce.
What are nachos? Little tortillas with meat, cheese and lettuce.
But seriously. Mexican food is food from Mexico.
And it's good.
:D