Nomen dubium

A nomen dubium is Latin for "doubtful name" (plural nomina dubia). It is a scientific name in zoology which is of unknown or doubtful use.
With a "nomen dubium" it may be impossible to decide whether a specimen belongs to that group or not. This may happen if the original type specimen is lost or destroyed. The zoological and botanical codes allow for a new type specimen, or neotype, to be chosen in this case.
A name may also be considered a "nomen dubium" if its name-bearing type is fragmentary or lacking important diagnostic features. This is often the case for species known only as fossils. To preserve stability of names, the International Code of Zoological Nomenclature allows a new type specimen, or neotype, to be chosen for a "nomen dubium" in this case.
It is one of a number of terms which are used in biological taxonomy.