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, grilled, or flame broiled. Hamburgers are often served with cheese, lettuce, tomato, onion, pickles, bacon, or chiles; condiments such as ketchup, mayonnaise, mustard, relish, or "special sauce"; and are frequently placed on sesame seed buns. A hamburger topped with cheese is called a cheeseburger.The term "burger" can also be applied to the meat patty on its own, especially in the United Kingdom, where the term "patty" is rarely used, or the term can even refer simply to ground beef. The term may be prefixed with the type of meat or meat substitute used, as in "turkey burger," "bison burger," or "veggie burger."The term "burger," a back-formation, is associated with many different types of sandwiches, similar to a (ground meat) hamburger, but made of different meats such as buffalo in the buffalo burger, venison, kangaroo, turkey, elk, lamb or fish like salmon in the salmon burger, but even with meatless sandwiches as is the case of the veggie burger.Louis Lassen of Louis' Lunch, a small lunch wagon in New Haven, Connecticut, is said to have sold the first hamburger and steak sandwichin the U.S. in 1900. New York magazine states that "The dish actually had no name until some rowdy sailors from Hamburg named the meat on a bun after themselves years later," noting also that this claim is subject to dispute. A customer ordered a quick hot meal and Louis was out of steaks. Taking ground beef trimmings, Louis made a patty and grilled it, putting it between two slices of toast. Some critics like Josh Ozersky, a food editor for New York Magazine, claim that this sandwich was not a hamburger because the bread was toasted.Hamburgers are usually a feature of fast food restaurants. The hamburgers served in major fast food establishments are usually mass-produced in factories and frozen for delivery to the site. These hamburgers are thin and of uniform thickness, differing from the traditional American hamburger prepared in homes and conventional restaurants, which is thicker and prepared by hand from ground beef. Most American hamburgers are round, but some fast-food chains, such as Wendy's, sell square-cut hamburgers. Hamburgers in fast food restaurants are usually grilled on a flat-top, but some firms, such as Burger King, use a gas flame grilling process. At conventional American restaurants, hamburgers may be ordered "rare," but normally are served medium-well or well-done for food safety reasons. Fast food restaurants do not usually offer this option.The McDonald's fast-food chain sells the Big Mac, one of the world's top selling hamburgers, with an estimated 550 million sold annually in the United States. Other major fast-food chains, including Burger King (also known as Hungry Jack's in Australia), A&W, Culver's, Whataburger, Carl's Jr./Hardee's chain, Wendy's (known for their square patties), Jack in the Box, Cook Out, Harvey's, Shake Shack, In-N-Out Burger, Five Guys, Fatburger, Vera's, Burgerville, Back Yard Burgers, Lick's Homeburger, Roy Rogers, Smashburger, and Sonic also rely heavily on hamburger sales. Fuddruckers and Red Robin are hamburger chains that specialize in the mid-tier "restaurant-style" variety of hamburgers.Some restaurants offer elaborate hamburgers using expensive cuts of meat and various cheeses, toppings, and sauces. One example is the Bobby's Burger Palace chain founded by well-known chef and Food Network star Bobby Flay.Hamburgers are often served as a fast dinner, picnic or party food and are often cooked outdoors on barbecue grills.