What is Marinara Sauce? That's a good one. And I can tell you there is no one single definitive answer. Doesn't exists, unlike, Amatriciana or Bolognese Sauce which both can have variations, they are still both pretty defined and the variations come after what defines a Bolognese or Amatriciana Sauce.
Well, one thing that a Marinara Sauce is, it's a Tomato Sauce, a type of Tomato Sauce and it will vary according to who makes it.
Italians (in Italy) refer to Marinara not as a Sauce but in association with a recipe as in
Spaghetti alla Marinara. this translates to Mariner's Spaghetti or in the style of the mariner, or "Sailor," and is of Southern Italy and Naples in particular. Southern Italian Spaghetti alla Marinara does not contain any Seafood as some might think.
Folklore has it that, Italian Sailors developed Marinara Sauce to cook on ships, as the high-acid content in tomatoes helped to preserve it well. Another theory is that the wives of Neapolitan Sailors cooked Spaghetti alla Marinara for their husbands when they returned from sea.
So what is Marinara Sauce? Renowned Cookbook author and Restaurateur Lidi Bastianich says of marinara sauce, "The difference between marinara sauce and tomato sauce is this: Marinara is a quick sauce, seasoned only with garlic, pepper, and, if you like, basil or oregano. The pieces of tomato are left chunky, and the texture of the finished sauce is fairly loose. Tomato sauce, on the other hand, is a more complex affair, starting with puréed tomatoes and seasoned with onion, carrot, celery, and bay leaf, and left to simmer until thickened and rich in flavor."
Marinara Sauce is widely used in Italian-American Cuisine, and the sauce varies from person to person and, cook-to-cook, chef-to-chef, restaurant to restaurant, "there is no one single exacting specific recipe, but all usually have Olive Oil, Garlic, Tomato, Pepperoncino, and Basil and or Oregano. Oregano seems to be the biggest single factor in what a Marinara Sauce actually is, as many versions of Marinara Sauce seem to have Oregano included in it, which is not usually present in true Italian (of and from Italy) Tomato Sauce, or Sugo al Pomodoro. One other factor, is that Marinara Sauce is cooked quickly, in about 10 minutes as opposed to 45 minutes or longer for regular Tomato Sauce.
OK, now, my Marinara Sauce, what I think it is, and how I make it. Remember, I am of Italian-American descent. I cooked professionally for 20 years, in French, then Italian Restaurants. To me, the way I was taught and what I think is the best tasting Marinara Sauce is as follows. To make Marinara Sauce, I already have my base, regular Tomato Sauce that I have made previously. When I was in a restaurant and someone wanted Marinara Sauce, this is the one we made. We'd use about a cup of our regular tomato sauce that was always on hand. When we got an order for Spaghetti Marinara, we'd put some Olive Oil and a single serving pan. Heat it, add a good amount of chopped fresh Garlic. Cook the garlic, add a bit of Pepperoncino (Red Pepper Flakes) and a little dried Oregano. This was our flavoring base, and would considerably add much flavor to the base Tomato Sauce, making for a quite tasty Marinara. Once the garlic has cooked to where it just starts to brown a bit, you add the Tomato Sauce and heat through. Once your spaghetti has finished cooking, you drain it, drop it in the pan with your Marinara Sauce, adding a bit of the pasta cooking water, toss the pasta (mix) and serve. Voila, Spaghetti Marinara, my version and the one one most excepted as Marinara, though there are others. This is not the defining Marinara Sauce Recipe, but I believe the one most widely used, and no matter, I can tell you it's dam tasty and, I always get raves whenever I make it. Basta!