species

A taxonomic level of natural history classification. It describes a group of organisms similar in essential features, capable of mating* with members of opposite sex to produce fertile offspring. In nomenclature, the genus is generally capitalized; the species is in lower case. * Excluding infertile individuals of the species. It may also be used in reference to members of a class of molecules (i.e. reactive oxygen species).

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999