Glossary entry

n.
Modifications of available names throughout a taxonomic group by the addition of a standard prefix or suffix in order to indicate that the taxa named are members of that group [Art. 1.3.7]. Zoological formulae are excluded from the provisions of the Code. The suffixes of family-group names denote ranks, not taxonomic groups, and do not form zoological formulae.

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