A pupusa is a Central American - usually Salvadorean - food. It's corn tortillas stuffed with a filling - plain cheese, or meat and cheese, or veggies - a spicy tomato-based sauce, and cortado, which is a spicy cabbage-pepper relish.
The tortillas are not the thin Mexican-style ones; they are more like the soft thick masa cakes that make up a tamale. The corn cake is stuffed with filling and then fried in a pan to make the pupusa!