Biological classification is a form of scientific taxonomy. It has had several definitions in phylogenetic taxonomy. It involves, or is related to, biological classification, scientific taxonomy and phylogenetics. This opened up discussions on the taxonomy and phylogeny of this and related species. The industry and sector follow the Industry Classification Benchmark taxonomy. The taxonomy of the genus is complex. Birds are categorised as the biological class Aves in Linnaean taxonomy. This list contains 851 species according to the Clements taxonomy. This process is crucial to biological taxonomy. A unified taxonomy (a universal system for classifying viruses) has been established. Another application of "k"-mers is in genomics-based taxonomy. "-aceae", a standardized suffix for plant family names in modern taxonomy. The taxonomy of protists is still changing. For a fuller treatment of this taxonomy, see the vertebrate article. Differences within languages directly correlate to differences in emotion taxonomy.