A species is most commonly defined as a group of organisms that can interbreed in nature and produce fertile offspring. This is known as the biological species concept. Species are characterized by reproductive isolation from other such groups, meaning members of one species typically cannot successfully reproduce with members of another species.
Other species concepts include defining species by shared physical features (morphological species concept), ecological niche (ecological species concept), genetic similarities, or evolutionary history. Despite these variations, the core biological species definition remains widely used because of its focus on reproduction and fertility of offspring.
In summary, a species is a fundamental biological classification unit consisting of organisms that are capable of breeding among themselves and producing fertile offspring, and that are reproductively isolated from other such groups.
