The native external format that Microsoft supports for Term Sets is CSV files, which are limited in the amount of metadata and functionality that is provided. To enhance the experience of import, export or "backup" of Term Store elements, support for SKOS (*.rdf files) is included. More information about this file format can be learned from the following link (external link): http://www.w3.org/2009/08/skos-reference/skos.html.
Some of the advantages to using SKOS rather than CSV:
·SKOS can include all terms sets within a selected term group
·SKOS includes additional metadata properties like translations, synoymns and custom properties
·SKOS is more universally supported outside of SharePoint Term Stores
NOTE: Managed and Faceted Navigation is not currently supported for either Export to and Import from SKOS.