A hamburger, beefburger or burger 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, barbecued, or flame broiled. Hamburgers are often served with cheese, lettuce, tomato, bacon, onion, pickles, or chiles; condiments such as mustard, mayonnaise, ketchup, relish, or “special sauce”; and are frequently placed on sesame seed buns. A hamburger topped with cheese is called a cheeseburger. (source)