Glossary entry

A concept of a taxon which is denoted by an available name (e.g. Mollusca, Diptera, Bovidae, Papilio, Homo sapiens). Each nominal taxon in the family, genus or species groups is based on a name-bearing type (although in the latter two groups such a type may not have been actually fixed).

Source:
International Commission on Zoological Nomenclature (1999) International Code of Zoological Nomenclature. Fourth Edition. - International Trust for Zoological Nomenclature, XXIX + 306 pp.

See also:
nominal family-group taxon
nominal genus