call number

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

• noun A number used in libraries to classify a book and indicate its location on the shelves.

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

• noun library science An identification number, usually consists of a combination of numbers and characters, used to identify and locate materials within a library.

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

• noun a mark consisting of characters written on a book; used to indicate shelf location