From BC Canada, here a casserole is a whole meal in one pan, baked in the oven. It will have protein, starch and vegetables. If you are asked to bring a hot dish to a pot luck, it could be a casserole, but generally would mean a hot vegetable dish, such as mashed potatoes, creamed corn etc.
http://www.etymonline.com/index.php?term=casserole one definition.
What I call other foods depends more on how I serve them.
Goulash is always served on noodles.
Stew is served in a bowl generally with home made biscuits, but sometimes bread on the side.
Meat pie is stew served in a pie crust. But with more vegies on the side.
Shepherds pie is not a casserole, because I serve vegies on the side. I know this makes not sense at all.