In Italy there is sugo, and there is salsa. Sugo derives from succo (juices) and refers to pan drippings from the cooking of meats, so "sugo" is used for rich meat-based sauces along with the lines of sugo alla Bolognese, or thick vegetable sauces. These often, though not always, are made to eat with pasta. A salsa, on the other hand, is a semi liquid-to-liquid raw or cooked sauce that's used as a condiment. It can go over pasta, for example, pesto alla genovese, but can also be used to season other dishes. For example, salsa verde is wonderful over boiled meats or potatoes, as is mayonnaise (salsa maionese in many cookbooks). If a sauce is especially delicate, it may be called "salsina."
The passage from sugo/salsa in Italian to sauce/gravy in English must have occurred when immigrant families settled into new neighborhoods in the U.S. and is, we suspect, an Italian-American family/neighborhood tradition more than anything else. Some immigrants translated the Italian name for what they put on their pasta as "gravy," while others translated it as "sauce," and the translations have been passed down through the generations, becoming ingrained in the process. People get amazingly passionate over things like this.
Another reader, Tony Smith, contributed these comments: "Simply put, 'sauce' is quickly made, i.e., salsa di pomodoro, pesto, etc.gravy takes all day to cook." He went on to say that he thinks of "gravy" as something along the lines of a chunk of meat that's stewed, and consumed as a second course (secondo), while the drippings are used to season pasta, risotto, gnocchi, or even mashed potatoes. As an example of a ragù, he suggests the Ligurian tocco, which is essentially a pot roast with a rich sauce that generally goes over pasta.
This isn't what we think of as a ragù—in Tuscany; it's a meat sauce made from ground meat, along with the lines of sugo alla Bolognese. However, just because a word means one thing in one part of Italy, there's nothing to say it doesn't mean something completely different in another region. So we looked up "ragù" in Antonio Piccinardi's Dizionario di gastronomia. He says:
"Ragù: A word of French origin that is applied to dishes that differ considerably, but share as a common characteristic the use of meat that's cooked for a long time in a sauce, which is generally destined to go over pasta. There are two main kinds of ragù: one is made with ground meat, and the other from a single piece of meat slowly cooked for a very long time, to which other ingredients can be added. Also, many dishes typical of the southern Regions are called al ragù, for example, carne al ragù or braciole al ragù, which consist of slabs of meat of varying size, rolled up around flavoring agents and cooked slowly.
The first type of ragù includes dishes of the Emilian tradition, as well as those from Bari or Sardegna, while the second group includes all the Southern Italian dishes."
Since Bari is in Puglia, which is certainly in the south, and Sardegna is generally lumped in with the southern regions, it's obvious that the breakdown between the ground meat and chunk-of-meat types of ragù is not regional, but local.
Since we associate the word "gravy" with meat drippings thickened with butter and flour (something that's not at all common in Italy, though we have encountered it in the Piemonte region), we call what goes over pasta "sauce" when we refer to it in English. But as is all-too-often the case with Italian food, there's no right or wrong answer here.