What is type?

When publishing a new species, a taxonomist needs to describe it not by imagination or guess work but by real examples. The original specimens used in a new-species publication are termed type series. To be a voucher standard and to avoid misidentification, a specimen will be chosen as a holotype from the type series. The rest become paratypes of this holotype, accordingly. This process is termed "type fixation". Apart from holotypes, syntypes, lectotypes, and neotype are termed "name bearing type" in the sense of International Code of Zoological Nomenclature (ICZN). Different name bearing types are dedicated to different conditions, respectively. A name bearing type is representative of the name it bears. That is, all nomenclature changes have to be based on the name bearing types. Paratypes, though not technically name bearing types, are still valuable references to identification.

The definition of types in ICZN:

Term Definition
allotype A term, not regulated by the Code, for a designated specimen of opposite sex to the holotype.
cotype A term not recognized by the Code, formerly used for either syntype or paratype, but that should not now be used in zoological nomenclature.
holotype The single specimen designated or otherwise fixed as the name-bearing type of a nominal species or subspecies when the nominal taxon is established.
lectotype A syntype designated as the single name-bearing type specimen subsequent to the establishment of a nominal species or subspecies.
neotype The single specimen designated as the name-bearing type of a nominal species or subspecies when there is a need to define the nominal taxon objectively and no name-bearing type is believed to be extant. If stability and universality are threatened, because an existing name-bearing type is either taxonomically inadequate or not in accord with the prevailing usage of a name, the Commission may use its plenary power to set aside that type and designate a neotype.
paralectotype Each specimen of a former syntype series remaining after the designation of a lectotype.
paratype Each specimen of a type series other than the holotype.
syntype Each specimen of a type series from which neither a holotype nor a lectotype has been designated. The syntypes collectively constitute the name-bearing type.
topotype A term, not regulated by the Code, for a specimen originating from the type locality of the species or subspecies to which it is thought to belong, whether or not the specimen is part of the type series.
type A term used alone, or forming part of a compound term, to denote a particular kind of specimen or taxon.

  *Source: http://www.nhm.ac.uk/hosted-sites/iczn/code/index.jsp?booksection=glossary&nfv=true