A hamburger, or simply burger, is a food consisting of fillings—usually a patty of ground meat, typically beef—placed inside a sliced bun or bread roll. Hamburgers are often served with cheese, lettuce, tomato, onion, pickles, bacon, or chilis; 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 patty topped with cheese is called a cheeseburger.