The meat sauce listed with lasagne sheets as a main ingredient of lasagna is ragù.
Ragù is a family of Italian meat sauces, commonly made with ground or finely chopped meat, vegetables and cooking liquid. In the best-known Bolognese style, the sauce may include beef and pork, onion, carrot, celery, butter, tomatoes and other seasonings. It is layered between pasta sheets in lasagne rather than simply poured over them.
Lasagne alla bolognese traditionally combines lasagne sheets with ragù, béchamel sauce and Parmesan cheese. This northern Italian version is especially associated with Bologna and Emilia-Romagna. Other regional lasagne recipes use different combinations: Neapolitan lasagne may include ragù, mozzarella, ricotta and small meatballs.
Ragù is often confused with any tomato sauce, but the defining idea is the meat-based preparation. Marinara is generally a tomato sauce without the same meat-sauce identity; carbonara is an egg-and-cheese pasta preparation; pesto is a herb-and-nut sauce.