Tomato sauce
A tomato sauce is any of a very large number of sauces made primarily out of tomatoes, usually to be served as part of a dish (rather than as a condiment). Tomato sauces are common for meats and vegetables, but they are perhaps best known as sauces for pasta dishes.
Tomatoes have a rich flavour, a high liquid content, very soft flesh which breaks down easily, and the right composition to thicken up into a sauce when they are cooked (without the need of thickeners like roux). All of these make them ideal for simple and appealing sauces.
The simplest tomato sauces consist just of chopped tomato flesh (with the skins and seeds optionally removed), cooked in a little olive oil and simmered until it loses its raw flavour, and seasoned with salt.
Water (or another, more flavorful liquid such as stock or wine) is often added to keep it from drying out too much. Onion and garlic are almost always sauteed at the beginning before the tomato is added. Other seasonings typically include black pepper, basil, oregano, and parsley. Ground or chopped meat is also common.
Italian tomato sauces
The tomato has been central to Italian cuisine since its introduction from the Americas. Outside of Italy, this perception can be quite exaggerated: many people know little of Italian cuisine beyond pasta with tomato sauce. Italian varieties of tomato sauce range from Puttanesca sauce, seasoned with anchovies, capers, chili peppers and black olives, to Bolognese sauce, a predominantly ground-meat sauce which normally contains a small-to-moderate amount of tomato. Some Italian Americans on the East Coast refer to tomato sauce as gravy, especially sauces with a large quantity of meat simmered in them, similar to the Italian Neapolitan ragù.
Indian tomato sauces
Indian curry, especially as it has been exported out of India, is recognizable for heavily spiced sauces, often made from a tomato base..