What is "submarine sandwich"?

A submarine sandwich, also known as a sub, hoagie, or hero, is a type of sandwich that is made on a long, cylindrical roll, typically made from Italian or French bread. The roll is sliced lengthwise and filled with a variety of meats, cheeses, vegetables, and condiments. The fillings for a submarine sandwich can vary widely and may include ham, turkey, roast beef, salami, provolone cheese, lettuce, tomato, onion, mayonnaise, mustard, and oil and vinegar dressing. The sandwich is often served cold, but can also be heated in an oven or on a griddle to melt the cheese and warm the meat. Submarine sandwiches are a popular food item in many countries around the world, and can be found at delis, sandwich shops, and fast food restaurants. They are a satisfying and convenient meal that is perfect for a quick lunch or dinner on the go.