MLA differentiates between online books and eBooks:
Each is cited somewhat differently, although the core style elements still provide the basis for your citations.
From Washington State University- Citing eBooks and Online Books
An Online book is a book with a URL that you can access on a website or database like Project Gutenberg, Google Books, ProQuest Ebook Central, EBSCOhost eBooks, Early English Books Online, etc.
An E-book is "a book that lacks a URL and that you use software to read on a personal device or computer" (MLA Style Center FAQ). This includes books that one reads using a Kindle, EPUB, Nook, or SORA etc.