I believe the correct term for Velveeta is "processed American cheese product".
Many grocery products are identified by what is called a "standard of identity" -- which keeps manufacturers from calling a product what it is not.
The terminology for Velveeta describes it as "American" cheese -- as opposed to Swiss, Cheddar, etc. -- a "cheese product", i.e., including cheese plus other products (in Velveeta's case, milk protein solids) -- and "processed" -- having been melted, mixed with other ingredients (including emulsifiers)and fabricated.
So, yes, Velveeta is mostly cheese and its constitution has been altered. So, technically, it's not "cheese".
You are correct, sir! (or Ma’am!) I just looked at a box. I stand corrected. It sure is yummy, though....