Call number:

A number consisting of a classification number, a book number, and additional information that uniquely identifies the item.  The call number is printed on the label affixed to a bibliographic item, so that the item can be shelved and found.

The call number represents the shelf location of the item in the library's collections.  It is referred to as the call number because it can be used to request or call for a particular item.

Example:

Title:  Treasures of the Library of Congress

Call number:  Z733.U58G66 1991