Quick Answer: An e-reader, also called an e reader or e device, is a mobile electronic device that is designed primarily for the purpose of reading digital e-books and periodicals. Any device that can display text on a screen may act as an e-reader; however, specialized e-reader devices may optimize portability, readability, and battery life for this purpose. Their main advantage over printed books is portability: an e-reader is capable of storing thousands of books while weighing less than a single one. Another advantage is the convenience provided by add-on features.