The GBIF Backbone Taxonomy is a single, synthetic management classification with the goal of covering all names GBIF is dealing with. It's the taxonomic backbone that allows GBIF to integrate name based information from different resources, no matter if these are occurrence datasets, species pages, names from nomenclators or external sources like EOL, Genbank or IUCN. This backbone allows taxonomic search, browse and reporting operations across all those resources in a consistent way and to provide means to crosswalk names from one source to another.
See also: GBIF Introduces New Version of the Backbone Taxonomy (Sep 9, 2019). The new version of the taxonomy adds approximately 725,000 names, around 85 per cent of them animals. The update also adds 100,000 accepted species names not previously included in the backbone.