In biology, a genus (plural: genera) is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia. Genera and higher taxonomic levels such as families are used in biodiversity studies, particularly in fossil studies since species cannot always be confidently identified and genera and families typically have longer stratigraphic ranges than species.
The term comes from the Latin genus meaning "descent, family, type, gender", cognate with Greek: γένος – genos, "race, stock, kin".
The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. In the hierarchy of the binomial classification system, genus comes above species and below family.
Joseph Pitton de Tournefort (1656–1708), a French botanist, is considered "the founder of the modern concept of genera".
The scientific name of a genus may be called the generic name or generic epithet: it is always capitalized. It plays a pivotal role in binomial nomenclature, the system of biological nomenclature.