Mirepoix is used as the flavor base traditionally made with 50% onions, 25% carrots, and 25% celery. Mirepoix is the base for a wide variety o dishes including stocks, soups, stews, and sauces.
Similar flavor bases include the Italian soffritto, the Spanish and Portuguese sofrito, and the holy trinity (onions, celery, and bell peppers) to name a few.