Porridge is more like wetter oatmeal, but doesn't have to be oats. Cream of wheat probably classifies as a porridge. I prefer barley porridge.

Stew (and gumbo) is thicker than soup, the liquid being more like gravy, so potpies are kinda like a pastry full of stew often made as single servings.

Shepherd's pie can be that wet but isn't always and has a roof of mashed potatoes and no pastry. It's really not a pie at all.

If calzone and pierogi are dumplings then so are pastel and empanadas. Personally I'm fine with that.

If I'm wrong about any of these I would enjoy being corrected, but these are all things I cook with some regularity so my opinions are deeply held.