A(n) is a group of organisms that only reproduces with other members of their group.

A species is a group of organisms that only reproduces with other members of their group.

A species can be said to be organisms that produce offspring that are fertile, with members of their own group.

Organisms of the same species  tend to also have more characteristics  in common among themselves than with members of a different species.

Species that are similar tend to dwell in  similar habitats and usually share  an ancestor which more often than not is quite recent.

A species. They only reproduce with other members from the same species.