A hamburger (or burger) is a sandwich consisting of a cooked ground meat patty, usually beef, placed in a sliced bun or between pieces of bread or toast. Hamburgers are often served with various condiments, such as ketchup, mustard, mayonnaise, relish etc. as well as lettuce, tomato, onion, pickles, and cheese. Hamburgers are usually a feature of fast food restaurants. The hamburgers served in major fast food establishments are 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. Generally 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 fried, but some firms, such as Burger King use a grilling process. At conventional American restaurants, hamburgers may be ordered "rare", but normally are served well-done for food safety reasons. Fast food restaurants do not offer this option. The McDonald's fast-food chain sells a sandwich called the Big Mac, one of the world's top selling hamburgers. Other major fast-food chains â€“ 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, In-N-Out Burger, Five Guys, Fatburger, Burgerville, Back Yard Burgers, Lick's Homeburger, Roy Rogers, and Sonic â€“ also rely heavily on hamburger sales. Fuddruckers and Red Robin are popular hamburger chains that specialize in mid-tier "restaurant-style" variety of hamburgers. The "slider" style of mini hamburger is still popular regionally in the White Castle and Krystal chains. Some American establishments offer a unique take on the hamburger beyond what is offered in fast food restaurants, using upscale ingredients such as sirloin or other steak along with a variety of different cheeses, toppings, and sauces. Hamburgers are often served as a picnic and party food, cooked outdoors on barbecue grills. Raw hamburger may contain harmful bacteria that can produce food-borne illness such as Escherichia coli O157:H7, due to the occasional initial improper preparation of the meat, so caution is needed when handling it. Hamburger patties can be cooked rare, medium rare, medium, medium well, or well done. These terms refer to how thoroughly the meat is cooked, ranging from having a little bit of pink coloring to being dark brown, cooked almost to a crisp. However because of the potential for food-borne illness, it is recommended[who?] that hamburgers should be cooked to an internal temperature of 170Â°F (80Â°C). If cooked to this temperature, they will be well done.