EBooks or Electronic books are self-contained "executable" files of HTML. This HTML code can be in the form of a website that you have created or HTML code that you have specially prepared to compile into an .exe download file for distribution.
When downloaded, this file is installed independently on your client desktop. You can also read one among the 100 books to read before you Die on Amazon.
E-books are very similar to regular physical books in that they are rich in content. They are a huge source of information. Anything you can write in a physical book, you can write in an e-book. If your website is about tropical birds, why not write a tropical bird guide.
If your website is for web design, then you can write tutorials for beginners. E-books are basically packaged offline sites that give writers a lot of flexibility in how content is presented. E-books can be downloaded from your website at any time and stored and read offline.
Hyperlinks and built-in search engines improve navigation and allow readers to find articles of interest quickly and easily. E-books combine the functionality and purpose of physical books with sophisticated software.
E-books will play a very important role in the future of society as a whole. In short, ebooks are a way to own and read regular books without the physical pages / folders that come with regular books, not just an eco-friendly way to have no physical paper pages.