A bun is a small, sometimes sweet, bread or bread roll. Though they come in many shapes and sizes, they are most commonly hand-sized or smaller, with a round top and flat bottom.Buns are usually made from flour, sugar, milk, yeast and butter. Common varieties contain small fruit or nuts, are topped with icing or caramel, or filled with jam or cream. Some types of buns are filled with various meats."Bun" may also refer to particular types of filled dumplings, such as Chinese baozi.