Physical characteristics
The leopard is an agile and stealthy predator. Although smaller than the other members of the Panthera genus, the leopard is still able to take large prey given a massive skull that well utilizes powerful jaw muscles. Its body is comparatively long for a cat and its legs are short. Head and body length is between 125 and 165 cm (35 and 75 in), the tail reaches 60 to 110 cm (24 to 43 in). Shoulder height is 45 to 80 cm (18-31 in). Males are about 30% larger than females, weighing 37 to 91 kg (82 to 200 lbs) compared to 28 to 60 kg (62 to 132 lbs) for females. The larger-bodied populations of leopard are generally found in areas isolated from competing large predators, especially from dominant big cats like lions and tigers.
One of many spotted cats, a leopard may be mistaken for a cheetah or a jaguar. The leopard has rosettes rather than cheetah's simple spots, but they lack internal spots, unlike the jaguar. The leopard is larger and more muscular than the cheetah but slightly smaller than the jaguar. The leopard's black, irregular rosettes serve as camouflage. They are circular in East Africa but tend to be square-shaped in southern Africa.

Leopards have been reported to reach 21 years of age in captivity.

Variant coloration
A melanistic morph of the leopard occurs, particularly in mountainous areas and rain forests. The black color is heritable and caused by recessive gene loci. (While they are commonly called black panthers, the term is not exclusive to leopards; it also applies to melanistic jaguars.)
Melanistic leopards are particularly common on the Malayan Peninsula: early reports suggested up to half of all leopards there are black, but a 2007 camera-trap study in Taman Negara National Park found that all specimens were melanistic. Although the benefits of melanism are difficult to interpret, it may serve as camouflage in the rainforest habitat. Genetic research has found four independent origins for melanism in cats, suggesting that there must be some adaptive advantage. Another possibility is that the color variation is a relic adaptation to an epidemic; genes causing melanism can also affect the immune system.
In Africa, black leopards are much less common as melanism is not an adaptive advantage on the savanna: dark coloration provides poor camouflage and makes hunting difficult. Estimates are as low as one in 80 or 100. In the dense forests of the Ethiopian Highlands, however, the black leopard is much more common than in Africa generally; as many as one in five leopards may be melanistic.
Pseudo-melanism (abundism) occurs in leopards. The spots are more densely packed than normal and merge to obscure the background colour.
A pseudo-melanistic leopard has a normal background color, but its excessive markings have coalesced so that its back seems to be entirely black. In some specimens, the area of solid black extends down the flanks and limbs; only a few lateral streaks of golden-brown indicate the presence of normal background colour. Any spots on the flanks and limbs that have not merged into the mass of swirls and stripes are unusually small and discrete, rather than forming rosettes. The face and underparts are paler and dappled like those of ordinary spotted leopards. These melanistic leopards are often incorrectly referred to by the general population as "black panthers".
In a paper about panthers and ounces of Asia, Reginald Innes Pocock used a photo of a leopard skin from southern India; it had large black-rimmed blotches, each containing a number of dots and it resembled the pattern of a jaguar or clouded leopard. Another of Pocock's leopard skins from southern India had the normal rosettes broken up and fused and so much additional pigment that the animal looked like a black leopard streaked and speckled with yellow.
Most other colour morphs of leopards are known only from paintings or museum specimens. There have been very rare examples where the spots of a normal black leopard have coalesced to give a jet black leopard with no visible markings. They may form swirls and, in some places, solid black areas. Unlike a true black leopard the tawny background colour is visible in places. One pseudo-melanistic leopard had a tawny orange coat with coalescing rosettes and spots, but white belly with normal black spots (like a black-and-tan dog).
A 1910 description of a pseudo-melanistic leopard:
There is, however, a peculiar dark phase in South Africa, a specimen of which was obtained in 1885 in hilly land covered with scrub-jungle, near Grahamstown. The ground-colour of this animal was a rich tawny, with an orange tinge; but the spots, instead of being of the usual rosette-like form, were nearly all small and solid, like those on the head of an ordinary leopard; while from the top of the head to near the root of the tail the spots became almost confluent, producing the appearance of a broad streak of black running down the back. A second skin had the black area embracing nearly the whole of the back and flanks, without showing any trace of the spots, while in those portions of the skin where the latter remained they were of the same form as in the first specimen. Two other specimens are known; the whole four having been obtained from the Albany district. These dark-coloured South African leopards differ from the black leopards of the northern and eastern parts of Africa and Asia in that while in the latter the rosette-like spots are always retained and clearly visible, in the former the rosettes are lost – as, indeed, is to a considerable extent often the case in ordinary African leopards – and all trace of spots disappears from the blacker portions of the skin.

—Lydekker, R. (1910), Harmsworth Natural History

Another pseudo-melanistic leopard skin was described in 1915 by Holdridge Ozro Collins who had purchased it in 1912. It had been killed in Malabar, India that same year.
The wide black portion, which glistens like the sheen of silk velvet, extends from the top of the head to the extremity of the tail entirely free from any white or tawny hairs … In the tiger, the stripes are black, of a uniform character, upon a tawny background, and they run in parallel lines from the centre of the back to the belly. In this skin, the stripes are almost golden yellow, without the uniformity and parallelism of the tiger characteristics, and they extend along the sides in labyrinthine graceful curls and circles, several inches below the wide shimmering black continuous course of the back. The extreme edges around the legs and belly are white and spotted like the skin of a leopard … The skin is larger than that of a leopard but smaller than that of a full grown tiger.

—Collins, Holdridge Ozro (1915)

In May 1936, the British Natural History Museum exhibited the mounted skin of an unusual Somali leopard. The pelt was richly decorated with an intricate pattern of swirling stripes, blotches, curls and fine-line traceries. This is different from a spotted leopard, but similar to a king cheetah hence the modern cryptozoology term king leopard. Between 1885 and 1934, six pseudo-melanistic leopards were recorded in the Albany and Grahamstown districts of South Africa. This indicated a mutation in the local leopard population. Other king leopards have been recorded from Malabar in southwestern India. Shooting for trophies may have wiped out these populations.