A book is a written monograph of at least 49 pages. This is according to the UNESCO definition.

A book may have different forms, but in this definition is required to be readable. It is a hint for potential readers which equipment and environment is required to access the information contained in the book. Therefore audio books are not considered as books. Without a playing device and earphones it cannot be consumed at a working place without annoying team members.

There is no distinction between hard- or soft covered books or e-books. Nowadays most libraries have access to non-electronical and electronical versions. Some books may be readable online with a browser. Add a reference to each accessible form to the location property of the resource type.