American Cheese is not really "cheese"

American Cheese is a processed cheese, a combination of different cheeses and artificial ingredients in order to produce a more durable, uniform product.  Unlike other cheeses it melts uniformly (useful for things like cheeseburgers).

In the United States,^[2]it may not be legally sold as "cheese", and must be labeled as "processed cheese", "cheese product", or similar—e.g., "cheese food". At times even the word "cheese" is missing in the name on the label, e.g. "American slices" or "American singles".

http://en.wikipedia.org/wiki/American_cheese