In Africa and Asia, a black panther is a melanistic leopard. The animal is not a separate species: it is a leopard, Panthera pardus, whose body produces unusually large amounts of the dark pigment melanin.
Black leopards may look completely black in dim light, but their familiar rosettes are usually still visible when sunlight reaches the coat. Melanism is associated especially with forested habitats, where a darker coat may provide camouflage. In leopards, the trait is generally linked to a recessive genetic variant, so two normally colored parents can sometimes produce a black cub if both carry it.
The phrase “black panther” can cause confusion because it is a common name rather than a precise taxonomic label. In Central and South America, it usually refers to a melanistic jaguar, Panthera onca. Thus, the geographic wording in this question matters: African and Asian black panthers are leopards, while American black panthers are typically jaguars.
Black and spotted leopard cubs can occur in the same litter. The color form does not change the species’ behavior, diet or basic biology.