A females vagina or vaginal opening.
See cunt,pussy,lady lips and lettuce.
Derived from a mexican taco, which has meat inside it and "hot sauce". Mexicans usually eat tacos...
Man that gal spread her legs and said, "baby, my vertical taco is getting cold, eat it quickly- lick all the sauce and add after that add the mayonnaise!.....uh uh yeah oh damn uh uh huuuhhh hhuuuuuh euhhh", and so on.