The correct answer is - subspecies.
The subspecies represents an aggregate of phenotypically similar populations of a species. They inhabit a geographic subdivision of the species. They also are differing taxonomically from the other members of the species.
The subspecies are part of a species. They are able to mate with the other members of the species without any problems if they come to a situation like that, and produce healthy offspring. In general, the subspecies is pretty much the same as the species, just that it exhibits some specific physical traits that are not found in the rest of the members of the species.
A perfect example for this is the leopard. The African leopard has short and less dense fur, is larger, lighter in coloration, while the Amur leopard has much denser and longer fur, is slightly smaller, and is darker in coloration. Both of them are part of the same species, but exhibit specific physical traits that make them a subspecies.