What is a book?

Carl Sagan, Astronomer (original photo here)

“What an astonishing thing a book is. It's a flat object made

 from a tree with flexible parts on which are imprinted lots of

 funny dark squiggles. But one glance at it and you're inside

 the mind of another person, maybe somebody dead for

thousands of years. Across the millennia, an author is 

speaking clearly and silently inside your head, directly to you. 

Writing is perhaps the greatest of human inventions, binding

 together people who never knew each other, citizens of 

distant epochs. Books break the shackles of time. A book is 

proof that humans are capable of working magic.” ― Carl Sagan