A cheeseburger is a hamburger containing cheese. The term itself is a portmanteau of the words "cheese" and "hamburger." The cheese is usually sliced, then added a short time before the hamburger finishes cooking to allow it to melt. In fast food restaurants, the cheese that is added to a cheeseburger is typically American cheese, but there are many other variations. Mozzarella, blue cheese, pepper jack, and especially cheddar are popular choices.