reference book

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A book, such as a dictionary or encyclopedia, to which one can refer for authoritative information.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A book providing factual information.
• noun libraries such a book that may not be borrowed.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a book to which you can refer for authoritative facts