An online catalog is a database that contains information about the materials in a library’s collection. It can include books, e-books, DVDs, CDs, and other types of materials. An online catalog allows patrons to search for materials by title, author, subject, and other criteria. It typically provides information about the location of a particular item within the library, as well as its availability (e.g., whether it is currently checked out or on the shelf). Many online catalogs also allow patrons to place holds on materials and renew items that they have checked out. An online catalog is often accessed through a library’s website and is an important tool for helping patrons find and access the materials they need.