A
holotype is a single physical example (or illustration) of an
organism, known to have been used when the
species (or lower-ranked
taxon) was formally described. It is either the single such physical example (or illustration) or one of several such, but explicitly designated as the holotype. Under the
International Code of Zoological Nomenclature (ICZN), a holotype is one of several kinds of
name-bearing types. An
isotype is a duplicate of the holotype.