The E-Book is a publication that is an exists in data form.
It may or may not exist as a printed edition.
Tim Challies provides two posts comparing the relative strength of data and printed books:
5 Reasons Books Are Better Than E-Books
1. I Can Truly Own a Book
2. I Can Loan a Book
3. A Book Offers an Experience
4. A Book Is a Single-Tasking Device
5. I Can Buy a Used Book
5 Reasons E-Books Are Better Than Books
1. Searchability
2. Portability
3. Versatility
4. Preservation
5. Cost
Then Challies summarises his thoughts on what to think about while embracing new technology.
Books & E-Books, Media & Messages