An electronic book (or e-book) is a book publication made available in digital form, consisting of text, images, or both, readable on the flat-panel display of computers or other electronic devices. Although sometimes defined as "an electronic version of a printed book" some e-books exist without a printed equivalent. Commercially produced and sold e-books are usually[dubious – discuss] intended to be read on dedicated e-reader devices. However, almost any sophisticated computer device that features a controllable viewing screen can also be used to read e-books, including desktop computers, laptops, tablets and smartphones.