Divide by Nought

The distinction is made less and less these days, but at one time there was a content, or subject matter, difference between paperbacks (aka trade paperbacks) and mass market paperbacks.  The types of books made into mass market paperbacks were generally of a more popular type.  While the content of trade paperbacks was generally reserved for more “educated” materials and literature.  At this point it’s pretty much just the physical size, materials and binding used; which are smaller and cheaper for the mass market versions.