A hamburger is a sandwich consisting of one or more cooked patties of ground meat, usually beef, placed inside a sliced bread roll or bun. The patty may be pan fried, grilled, smoked or flame broiled. Hamburgers are often served with cheese, lettuce, tomato, onion, pickles, bacon, or chiles; condiments such as ketchup, mustard, mayonnaise, relish, or a "special sauce", often a variation of Thousand Island dressing; and are frequently placed on sesame seed buns. A hamburger topped with cheese is called a cheeseburger.