Thick buttery crust rolled up the edges of a DEEP pan. Crust, then LOTS of cheese, then chunky crushed tomato sauce on top. Sprinkled with parmesan. Carmelized cheese at the upper edge of the crust = bonus. If it is going to have fillings, it should be an obscene amount of chicago style italian sausage below the cheese layer.
Pizzeria Uno Chains = Not quite deep dish, it's cooked on a rack
Old Chicago = Pan pizza (Not the same)
Some places serve "Chicago Deep Dish" around here but it has another layer of crust ontop of the cheese, so it is "stuffed". This is how Giordano's in Chicago makes their pie as well so it could maybe be called traditional chicago style, but it isnt deep dish, it is stuffed.
Chicago Deep Dish and Dogs made a RAGIN good pie until they closed it could hold it's own against chicago anyday...
The wiki explains it all, has a picture of Geno's East Deep Dish pie (My personal fav!):