Any collection of foods, usually meat and vegetables, heated in a broth or stock, is considered a casserole.
Casseroles vary from traditional quiches and Shepherd's pie to the more experimental breakfast and dessert casseroles.
Tuna Casserole
Though seafood is not a typical ingredient in most casseroles, tuna casserole is a steady entrant in American cuisine. Most recipes use canned tuna and fresh mushrooms. Tuna casserole tends to be thicker, resembling a solid dish much more than a stew, and thus usually includes cream soups as its base rather than thinner broths.
Casseroles vs. Savory Pies
As both dishes typically contain mixed meat and vegetables, the differences between casseroles and savory pies may be minimal. Though savory pies will frequently have crusts on both top and bottom, casserole does not. Shepherd's Pie, thus, is a pie in name only, as it is rarely cooked using a crust and is considered primarily and casserole.
The French origin of the word suggests that any recipe cooked using a "casserole" dish may be considered a casserhole, regardless of the ingredients.
