A hamburger (or cheeseburger when served with a slice of cheese) is a sandwich consisting of one or more cooked parties of ground meat, usually beef, placed inside a sliced bread roll or bun.  Hamburgers may be cooked in a variety of ways, including pan-frying, barbecuing, and flame-broiling.  Hamburgers are often served with cheese, lettuce, tomato, bacon, onions, pickles, and condiments such as mustard, mayonnaise, and ketchup.
The term "burger" can also be applied to the patty on its own, especially in the UK where the term "patty" is rarely used.  The term may be prefixed with the type of meat or meat substitute used, as in "turkey burger", "bison burger", or "veggie burger".
Hamburgers are sold at fast-food restaurants, diners, and specialty and high-end restaurants (where burgers may sell for several times the cost of a fast-food burger).  There are many international and regional variations of the hamburger and one of the most famous chains is located nearby.