I remember that term from early elementary school. Moving from literal children's bedtime type story books to books with chapters, i.e. chapter books, was something that was applauded for five and six year old kids. But very shortly after that we shifted to just calling them books because all books except toddler books have chapters.
Me either, and I don't watch or read manga or amine, is that even considered a book? I thought it was what Japanese and neck beard incels jerked off to.