An online library catalog or OPAC (online public access catalog) is a searchable, computerized database of items owned or subscribed to by a library. It will allow you to perform familiar searches by author, title, keyword, and Library of Congress Subject Headings (LCSH). There are also less common search options available. Each record in the database describes an item and provides information about its location, call number and availability is the library system. The OPAC for UK Libraries is called InfoKat Discovery Library Catalog.