Term for a formal category in the taxonomic hierarchy as well as for a particular taxon of that the category. Scientific names for species are always Latin binominals. What constitutes a species in practice, or how we recognize a species in nature, is a matter of current debate among biologists. As a result, several species concepts have been formulated. The best known concept, the biological species concept, recognizes as species groups of individuals that are reproductively isolated and are capable of interbreeding among themselves.