A species (pl. species) is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction

It is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity.

A species is a set of populations with a unique evolutionary origin and history, made up of similar individuals who can interbreed fertilely and are reproductively isolated from other similar groups.