online public access catalogue (Internet) (OPAC)

An Online Public Access Catalogue (OPAC) is an electronic library catalog that is publicly accessible as part of a portal. All publications and media are recorded in such a library catalog.

Library catalogs can be searched by means of online research. The entries go far beyond publications in journals or reference books and include CD-ROMs, audios and videos. Online searches can be based on authors, publication title, ISBN number, publisher, or specific keywords. It is also usually possible to linksearch algorithms. For example, a searcher can link the name of an author to a search word or to a year of publication.