A MARC 21 format is a set of codes and content designators defined for encoding machine-readable records. Formats are defined for five types of data: bibliographic, holdings, authority, classification, and community information.
1.3.1. MARC 21 Format for Bibliographic Data contains format specifications for encoding data elements needed to describe, retrieve, and control various forms of bibliographic material. The MARC 21 Format for Bibliographic Data is an integrated format defined for the identification and description of different forms of bibliographic material. MARC 21 specifications are defined for books, serials, computer files, maps, music, visual materials, and mixed material. With the full integration of the previously discrete bibliographic formats, consistent definition and usage are maintained for different forms of material.
1.3.2. MARC 21 Format for Holdings Data contains format specifications for encoding data elements pertinent to holdings and location data for all forms of material.
1.3.3. MARC 21 Format for Authority Data contains format specifications for encoding data elements that identify or control the content and content designation of those portions of a bibliographic record that may be subject to authority control.
1.3.4. MARC 21 Format for Classification Data contains format specifications for encoding data elements related to classification numbers and the captions associated with them. Classification records are used for the maintenance and development of classification schemes.
1.3.5. MARC 21 Format for Community Information provides format specifications for records containing information about events, programs, services, etc. so that this information can be integrated into the same public access catalogs as data in other record types.