A 'book' in Drupalish, the Drupal slang, is a content type which allows you to create static pages which are linked to each other through a hierarchical navigation system. On a book page you can use all the things that you can use in a Research Journal Entry (which is called 'blog' page in Drupalish). The content type book is useful for longer texts where you want to split content into different pages. As the navigation control is created by Drupal, this comes in very handy.
