Cheese on a Reuben is a classic sandwich made with SWISS cheese, corned beef, sauerkraut, and Thousand Island dressing, served on rye bread. The term 'Cheese on a Reuben' refers to the combination of ingredients, with SWISS cheese being the most prominent. SWISS cheese is a type of cheese that originated in Switzerland and is known for its distinctive holes. It has a mild, nutty flavor and is often used in sandwiches and other dishes.