Polpettone di carne normally refers to a very large meatball or slices of what we would call a meatloaf. Those pictured were on a local menu as “polpettone” so that’s how we will list them. Usually the word “polpette” would be used for a plate like this.
Polpette don’t have to be made of meat. You might come across Polpette di polpo, or octopus (meat)balls. Polpette can be entirely vegetarian as well; cucina povera brought us many clever interpretations of meatballs without that expensive meat.
You aren’t likely to find Italian restaurant menus featuring “spaghetti and meatballs”. This mythical American dish, iconic in the US, isn’t really a “thing” in modern Italian cooking. Yes, there are examples of tiny meatballs in some southern Italian pasta dishes, but the giant ones in Italy lie on the plates all by themselves. It’s better that way when you consider that you can order a very different pasta dish and then have meatballs in tomato sauce later in the meal.
In fact, when the second plate has a tomato sauce as its condiment, Italians will usually choose a non-tomato sauce on their pasta. Variety is the spice of life unless you’re in a place like Puglia in the warmer seasons when the tomatoes are so good you can’t stop eating things made with them.