Scalloped Potatoes and Au Gratin Potatoes

"Au Gratin" refers to the technique of a crunchy topping - typically bread crumbs. the technique can be used on quite a number of dishes.

you can do a creamy sauced thinly slice casserole of potato - many names attached thereto depending on additives.

top it with bread crumbs - preferably seasoned - and bingo you got "taters Au Gratin"

Dilbert is correct. However, people have come to expect cheese in au gratins (they think gratin is French for cheese). So to the average person the difference is au gratins have cheese, escalloped (scalloped) do not. Not correct, but generally accepted definition.