OPAC stands for Online Public Access Catalog. It is also known as the catalog, PAC, WebPAC, library catalog, and online catalog. OPACs generally contain records of all the items that are library catalogs, such as: books (print and/or electronic); journals (print and/or electronic); databases; maps; manuscript collections; etc. An OPAC is public (anyone can use it), and it allows the patron to search the library's collection, check course reserves, and check one's own library records -- from any computer connected to the internet.
You can click here to access the service.