The basic unit of biological classification in Linnean or neoLinnean systems. Several similar species comprise a genus, and populations within a species that have distinctive traits may be called subspecies, races, varieties, or forae. A species is commonly defined as a group of organisms capable of interbreeding and producing fertile offspring in nature. The concept is difficult to apply to prokaryotes or other organism that reproduce asexually, or to extinct organisms, and is also difficult to apply to organisms produced by genetic engineering or that live in artificial environments (as is true today of the vast majority of Terragen organisms). Further, even with extant naturally evolved organisms that reproduce sexually there are many edge cases. Nevertheless the essential concept has proven to be robust and the term is still used as a convenient label for types of organic life forms.
- Genus - Text by M. Alan Kazlev
In the Linnean system of classification, a monophyletic taxon of closely related and similar biological organisms. A genus contains one or more species. A group of similar genera forms a family. In the Linnean name of an organism, the first name is its genus, the second, the species.
- Linne, Carl - Text by M. Alan Kazlev
Swedish Old Earth Industrial Age botanist who formulated the binomial system of nomenclature as a means of classifying living organisms, a system that is still used across large portions of the Terragen Sphere.
- Neospecies - Text by M. Alan Kazlev
 In Evolution theory - a newly (naturally) evolved species.
 A gengineered species.
- Quasispecies - Text by Manfred Eigen in Anders Sandberg's Transhuman Terminology
A fuzzy distributions of genotypes characterizing a population of quickly mutating organisms, alifes, or molecules.