A black panther is typically a melanistic color variant of any Panthera species. Black panthers in Asia and Africa are leopards (Panthera pardus). Black panthers in the Americas are black jaguars (Panthera onca).
Since the it has been considered politically incorrect to call a black cat a black panther. The big black cats are black leopards or black jaguars and are not referred to as black panthers by anyone who knows anything about big cats.