Genus, in biology, category of classification of living things; specifically, a group of species (see Species and Speciation) closely related in structure and evolutionary origin. The position of a genus, in classification of the kingdoms of living forms, is below family or subfamily, and above species.

A genus name always differs from the name used for any other genus of living forms. An organism is named by assigning it a binomial, consisting of a genus name followed by a species name. In the scientific name of the tiger lily, Lilium tigrinum, for example, Lilium is the genus name and tigrinum is the species name. In zoological nomenclature, the genus and species names may be identical; the gorilla, for example, is Gorilla gorilla. In botanical nomenclature, the genus name may never be assigned as a species name. The scientific name applied to a family is always a modification of the name of one of the genera; the genus involved is termed the type genus. See Taxonomy.