When you wrap a tortilla around a delicious filling, that's a taco. Traditional tacos are usually made with spicy, seasoned meat and garnishes like salsa and avocado — but these days, people put all kinds of things in tacos.
Tacos were invented in Mexico before the Spanish arrived. In Mexican Spanish, taco means "light meal," but also "wedge" or "plug." Experts have made guesses about the indigenous roots of taco (like the Nahuatl word tlahco, "half" or "in the middle"), but this connection hasn't been proven. Today when you order a taco, it might come on a soft or crunchy fried tortilla, and be filled with meat, fish, vegetables, beans, cheese, or even tofu.