Ebooks, also called electronic books, digital books, full-text books, or online books, can be accessed 24/7 from any location.
Ebooks allow one to search the entire full-text of the books, which can be both an advantage and a disadvantage.
Google Books is a huge collection of scanned books.
Google Books should not be your first stop, however. Its strength is that you can search the full text across so many books. Google Books is also useful for previewing books, especially for reviewing the table of contents.
When searching Google Books, best to use "exact phrase searches", that is, glue your words/phrases together with " ".