An Online Public Access Catalog or OPAC (aka iPAC for Internet/Intranet Public Access Catalogue) is a computerized online catalog of the materials held in a library, or library system. The library staff and the public can usually access it at computers within the library, or from home. OPAC terminals began to replace card catalogs in many libraries in the 1980s. Since the mid-1990s, these systems have increasingly migrated to Web-based interfaces. OPACs are often part of an integrated library sy… (More on Opac)