“WorldCat is a database of bibliographic information created and continuously updated by some 25,000 OCLC member libraries around the world. WorldCat records describe specific works and contain a listing of institutions that own an item, referred to as “holdings.” Institutions use holdings information to create local catalogs, arrange interlibrary loans and conduct reference work.”

“WorldCat was created in 1971 so that libraries could share cataloging information from a central database, increasing workflow efficiency and the ability to locate and loan materials. It took the OCLC cooperative almost 34 years, from August 26, 1971 to August 11, 2005, to add 1 billion holdings in WorldCat. It has taken just seven years and eight months to add the next billion.” 

“WorldCat spans six millennia of recorded knowledge, from about 4800 B.C. to the present. It encompasses records for books, serials, sound recordings, musical scores, maps, visual materials, mixed materials and computer files.”

From OCLC Member Update [oclc@oclc.org]

“Find more about WorldCat on the OCLC website, and watch WorldCat grow as libraries around the world contribute to the database.”

(Holdings constitute a higher number than titles.  A(nother) holding is counted for each library that owns a title.