A casserole, from the French for “saucepan”, is a large, deep dish used both in the oven and as a serving vessel. The word casserole is also used for the food cooked and served in such a vessel, with the cookware itself called a casserole dish or casserole pan. In British English, this type of dish is frequently also called a bake, coinciding with the cooking techniqueused to cook casseroles.
The casseroles we know today are a relatively modern invention. Early 18th century casserole recipes consisted of rice that was pounded, pressed, and filled with a savoury mixture of meats such as chicken or sweetbreads. Some time around the 1870s this sense of casserole seems to have slipped into its current sense. Cooking in earthenware containers has always been common in most nations, but the idea of casserole cooking as a one-dish meal became popular in America in the twentieth century, especially in the 1950s when new forms of lightweight metal and glassware appeared on the market. By the 1970s casseroles took on a less-than sophisticated image.
*Info from Wikepedia