A hamburger, often known as a burger, consists of fillings—usually a patty of panfried or grilled ground meat, typically beef—placed inside a sliced bun, sesame seed bun, or bread roll. These patties are often served with lettuce, tomato, onion, pickles, bacon, or chilis, together in the bun or roll. The filling of the burger can be topped with condiments such as ketchup, mustard, mayonnaise, relish, or a "special sauce", often a variation of Thousand Island dressing. A burger with the patty topped with cheese is called a cheeseburger, in which case "hamburger" often refers to a burger without cheese. Under some definitions, a hamburger is considered a sandwich.