A list of the holdings of all the libraries in a library system, or of all or a portion of the collections of a group of independent libraries, indicating by name and/or location symbol which libraries own at least one copy of each item. When the main purpose of a union catalog is to indicate location, the bibliographic description provided in each entry may be reduced to a minimum, but when it also serves other purposes, description is more complete. The arrangement of a union catalog is normally alphabetical by author or title. IFLA maintains a Directory of National Union Catalogues.

See also: National Union Catalog, National Union Catalog of Manuscript Collections, virtual union catalog, and WorldCat.


From ODLIS, Online Dictionary for Libary and Information Science by Joan M. Reitz
http://lu.com/odlis/about.cfm