Chowder is a thick soup prepared with milk or cream, a roux, and seafood or vegetables. Oyster crackers or saltines may accompany chowders as a side item, and cracker pieces may be dropped atop the dish. New England clam chowder is typically made with chopped clams and diced potatoes, in a mixed cream and milk base, often with a small amount of butter. Other common chowders include seafood chowder, which often consists of fish, clams, and other types of shellfish; lamb or veal chowder made with barley; corn chowder, which uses corn instead of clams; various fish chowders; and potato chowder, which is often made with cheese. Fish, corn, and clam chowders are popular in North America, especially New England and Atlantic Canada.