Clam chowder day is an unofficial, one of food days adopted by the United States.
Clam chowder is a soup containing the axis and oysters, sometimes even pieces of potatoes and onions. Clam chowder is not acceptable to add vegetables, other than carrot (mainly for color). If you insist, you can add a little above or a bay leaf parsley garnish. The origin of clam chowder is cold US states bordering the sea, where you can catch the oysters. The dish popular variously primarily in San Francisco, New England, Manhattan and more.