A Mexican dish consisting mainly of a cheese-filled tortilla cooked on a comal is a quesadilla.
The basic preparation folds a corn or flour tortilla around cheese and heats it until the tortilla is warm and the cheese melts. Depending on the region, additional ingredients can include mushrooms, squash blossoms, huitlacoche, meat, vegetables, or stews. The tortilla may be cooked on a comal, fried, or prepared in other local styles.
The name comes from queso, the Spanish word for cheese, and cheese remains the defining ingredient in the classic understanding of the dish. However, Mexico City has a famous regional disagreement: quesadillas there may contain fillings without cheese unless the customer specifically orders cheese, while much of the rest of Mexico treats cheese as essential.
Outside Mexico, especially in the United States, quesadillas are often made with large flour tortillas and mixtures such as Monterey Jack, Cheddar, chicken, beans, or guacamole. Those versions are related, but they should not obscure the simpler Mexican model of a hot tortilla with a melted filling.