A genus is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.