A biological species consisting of overlapping subgroups, each of which can interbreed with the next, but which cannot freely interbreed when taken as a whole

(biology) A species which is in danger of becoming extinct throughout all or a significant portion of its range. / A class or kind whose continued existence is threatened.

(taxonomy) A scientific name at the rank of species, with two terms: the generic name (or generic epithet, the genus of the species) and the specific name (a term used only in zoology, never in botany, for the second part of a binomial) or the specific epithet (the term always used in botany, which can also be used in zoology).

(biology) A species that normally lives and thrives in a particular ecosystem. This can include any species that developed with the surrounding habitat, and can be assisted by or affected by a new species.

(biology) Any species that has been introduced to an environment where it is not native, and that has since become a nuisance through rapid spread and increase in numbers, often to the detriment of native species.

(taxonomy) A grouping of closely-related species that are treated like a single species for practical purposes.

(ecology) Any species of organism that is vulnerable to extinction in the near future

(ecology) A species that exerts a large, stabilizing influence throughout an ecological community, despite its relatively small numerical abundance.

(neologism) The experience of dysphoria associated with the feeling that one's body is of the wrong species.

(taxonomy) A species which has been designated as typical of a genus, and is chosen as the species according to which the genus is named.