"American" cheese is a cheddarlike variety, but it's less "bity," more mild in flavor. It's sold in bricks or in slices. I buy mine in packaged slices, but *not* the ones that are individually wrapped. Overpackaging is one of my economic/ecological bugaboos. You could certainly substitute *any* cheese for it, as long as it's not *processed!*

Yes, you can *get* American processed cheese, but that's got more carbs in it than "natural" cheese. I don't claim to know what they do to it, but it adds carbs to a food that has practically none in its natural state. I never was fond of processed cheese (or even better, "processed cheese food"--what does cheese *eat* anyway???) to begin with. Now I have a perfect reason *not* to buy it!

So, the corrolary to my answer to your real question is: Use whatever kind of cheese you like to have on burgers; substitutions are allowed!