A public domain book is one that was either never subject to copyright or whose legal copyright term has expired. It might be a novel like Moby Dick (first published in 1851), or an ancient work like Aristotle's observations on bees.
Books in the public domain are fully available in Google Books which means that you can page through the book from start to finish in your browser, or download a copy of the eBook as a PDF.
For users in the U.S., Google Books currently treats all books published after 1923 as protected by copyright. The display options for copyrighted books include No Preview, Snippet View, or Limited Preview.
You can see books in Full View if the book is out of copyright, or if the publisher or author has asked to make the book fully viewable. Full View allows you to view any page from the book, and if the book is in the public domain, you can download, save and print a PDF version. In the Advanced Book Search, you can limit your results to Full view only by selecting the corresponding radio button.
If the publisher or author has given Google permission, you can see a Limited Preview of pages from the book as a preview. When paging through the book, you will notice incomplete pages, and the following message between the available pages:
The Snippet View shows basic information about the book plus a few snippets – a few sentences to display your search term in context.
With No Preview Available you can only see basic information about the book, with no option to view pages or search the text, like in the example below.