A casserole by definition is a kind of stew or side dish that is cooked slowly in an oven. It has come to mean any dish that is baked in the oven in a deep dish, such as a cast iron skillet or casserole dish. u003cbr/u003eu003cbr/u003eCasseroles can have layers like a lasagna, even a deep dish pizza is considered a casserole (who knew!), but typically anything baked in the oven with a starchy binder (like these u003ca href=u0022https://www.thefreshcooky.com/best-potato-gratin/u0022u003ePotatoes Dauphinoiseu003c/au003e) and a combination of a protein and veggies is considered a casserole. (u003ca href=u0022https://www.masterclass.com/articles/what-is-a-casseroleu0022 target=u0022_blanku0022 rel=u0022noreferrer noopeneru0022u003esourceu003c/au003e)