The relevant information.
Quote: Pasteurized process cheese, for example, is made from one or more cheeses, such as cheddar or colby, and may have cream or anhydrous milkfat added. The cheese is blended and heated with an emulsifier—typically a sodium or potassium phosphate, tartrate, or citrate—and other optional ingredients such as water, salt, artificial color, and spices or other flavorings.
Pasteurized process cheese food is a variation of process cheese that may have dry milk, whey solids, or anhydrous milkfat added, which reduces the amount of cheese in the finished product. It must contain at least 51% of the cheese ingredient by weight, have a moisture content less than 44%, and have at least 23% milkfat.
Pasteurized process cheese spread is a variation on cheese food that may contain a sweetener and a stabilizing agent, such as the polysaccharide xanthan gum or the Irish moss colloid carrageenan, to prevent separation of the ingredients. The cheese must be spreadable at 70 F, contain 44 to 60% moisture, and have at least 20% milkfat.
So then in short Velveeta is 51% cheese mixed with an emulsifier, such as sodium or potassium phosphate, tartrate, or citrate, which can be up to 49% of the mix. So that settles it, Velveeta is 51% cheese, or half cheese if you round it off. It would be almost as accurate to call it "emulsifier" as it is to call it cheese.
"Pass the sodium phosphate... yum."
That settles it, Velveeta is not cheese, it's more like half cheese, and half undetermined other stuff that could be damn near anything.