Because its ingredients differ so much from those of "unprocessed"/raw/natural cheeses,
[1] American cheese can not be legally sold under the name (authentic) "
cheese" in the US. Instead, federal (and even some state) laws mandate that it be labeled as "
processed cheese", "cheese product", "cheese food", etc. As a result, sometimes even the
word "cheese" is absent, altogether, from the product's labeling in favor of, e.g., "American slices" or "American singles". In the United Kingdom, packs of individually wrapped slices are labeled as "singles",
[2] although they are commonly referred to as "cheese slices".