What does a union catalog represent?

A union catalog represents a comprehensive listing of the holdings from multiple libraries. This type of catalog allows users to see what materials are available across a variety of library collections, making it easier to locate items that may not be found in a single library's catalog. By compiling records from different libraries, a union catalog enables efficient resource sharing and collaboration among libraries, which ultimately benefits patrons by broadening access to diverse materials.

The other choices do not align with the definition of a union catalog. A list of books authored by a single writer is focused on individual authorship, while a record of government publications or a digital archive of rare books pertains to specific categories of materials. None of these options captures the essence of a union catalog, which is explicitly designed for showcasing the collective holdings of multiple libraries.