Panthera is a genus of the family Felidae and is where the name Panther obviously comes from.........There are only four cats in this genus.......tiger, lion, leopard and jaguar so any other cats cannot correctly be called Panther.......a black leopard can therefore be correctly called a black panther as could a black jaguar, tiger or lion (if there are any) but although common usage seems to include any black variety of wild cat, it is not "correct" to give the name Panther to species other than the four mentioned.
BTW.These four are the only four which can roar due to some modification to bones in the throat..........