The Italian sub, the hero, the hoagie, the grinder, and the wedge are five names for one sandwich, and the names are the most interesting thing about it, because the thing being named never changes. A long roll, split, shingled with cured pork and provolone, dressed with oil and something sharp. That is the entire genre. Capicola, salami, ham, and a hard or sharp provolone are the shared core, and the regional argument is never really about the meats. It is about the word, the roll, and the dress, and the word a person uses places them on a map more precisely than a zip code does.
The reason the same sandwich can carry five names and stay one sandwich is that the engineering underneath all five is fixed. The roll is the load-bearing decision: a crust with enough structure to carry a long, layered, oil-slicked filling without folding at the midpoint, and a crumb tender enough that it does not fight what is inside it. The meats are shingled, not stacked, so every bite delivers capicola and salami and ham and cheese together rather than a band of one at a time. The lettuce is shredded so it distributes an even cool crunch through the length. The oil and the vinegar or the hot pepper are not condiments dropped on top; they season and lubricate the dry cured interior so it reads as juicy from one end to the other. Built correctly, a foot of it holds together cold for an hour, which is the only thing the format was ever asked to do.
The variations are mostly nominal, and that is the point of treating this as a genre rather than a recipe. The Philadelphia hoagie, the New York hero, the New England grinder, and the Westchester wedge are the same cold Italian build under four local words, each with small dressing and bread differences locals will defend at length. The chain submarines standardized particular assemblies and shipped them nationally. The hot side, the parm and meatball builds, treats the roll as a vessel for a saucy filling and leans on a sturdier crust. Each of those is a codified sandwich with its own rules and its own followers, and each deserves its own article rather than being crowded in here, because the whole reason this family is interesting is that every position on the map thinks its name is the real one.