Originated in 1987 as the product of an Earth Science and Applications Data Systems workshop, as a step towards data system interoperability. GCMD DIF is a metadata file format. As the “container” for the metadata in the Committee on Earth Observation Satellites (CEOS) International Directory Network (IDN), it does not compete with other metadata standards.The metadata used by the GCMD is considered to be that set of attributes that are instrumental in helping users to determine if a data set meets their qualifications. The set of attributes (fields) and its associated syntax is known as the Directory Interchange Format (DIF). It has evolved over the years and serves the user community in the discovery of Earth science data.
Source for DIF: http://gcmd.nasa.gov/Aboutus/standards/
Source for What Is a DIF: http://gcmd.nasa.gov/User/difguide/whatisadif.html