This ambiguity around what a book is seems like an artificial one. Go to a bookstore or view the catalog in Apple Books. Those are books, even the $0.99 micro s

This ambiguity around what a book is seems like an artificial one. Go to a bookstore or view the catalog in Apple Books. Those are books, even the $0.99 micro stories one might find on, e.g., Kindle. Anything else might be a book, but probably not in a way that is useful or constructive to analyze in the context of sales.