The cheetah (Acinonyx jubatus) is an atypical member of the cat family (Felidae) that is unique in its speed, while lacking strong climbing abilities. The species is the only living member of the genus Acinonyx. It is the fastest land animal, reaching speeds between 112 and 120 km/h (70 and 75 mph) in short bursts covering distances up to 460 m (1,510 ft), and has the ability to accelerate from 0 to 103 km/h (64 mph) in three seconds, faster than most supercars. Recent studies confirm the cheetah's status as the fastest land animal.

The word "cheetah" is derived from the Sanskrit word citrakāyaḥ, meaning "variegated body", via the Hindi चीता cītā.

The genus name, Acinonyx, means "no-move-claw" in Greek, while the species name, jubatus, means "maned" in Latin, a reference to the mane found in cheetah cubs.

The cheetah has unusually low genetic variability and a very low sperm count, which also suffers from low motility and deformed flagella. Skin grafts between unrelated cheetahs illustrate this point in that there is no rejection of the donor skin. It is thought that it went through a prolonged period of inbreeding following a genetic bottleneck during the last ice age. It probably evolved in Africa during the Miocene epoch (26 million to 7.5 million years ago), before migrating to Asia. New research by a team led by Warren Johnson and Stephen O'Brien of the Laboratory of Genomic Diversity (National Cancer Institute in Frederick, Maryland, United States) has recently placed the last common ancestor of all existing species as living in Asia 11 million years ago, which may lead to revision and refinement of existing ideas about cheetah evolution. Now-extinct species include: Acinonyx pardinensis (Pliocene epoch), much larger than the modern cheetah and found in Europe, India, and China; Acinonyx intermedius (mid-Pleistocene period), found over the same range. The extinct genus Miracinonyx was extremely cheetah-like, but recent DNA analysis has shown that Miracinonyx inexpectatus, Miracinonyx studeri, and Miracinonyx trumani (early to late Pleistocene epoch), found in North America and called the "North American cheetah" are not true cheetahs, instead being close relatives to the cougar.

Although many sources list six or more subspecies of cheetah, the taxonomic status of most of these subspecies is unresolved. Acinonyx rex—the king cheetah (see below)—was abandoned after it was discovered the variation was only a recessive gene. The subspecies Acinonyx jubatus guttatus, the woolly cheetah, may also have been a variation due to a recessive gene. Some of the most commonly recognized subspecies include:

The cheetah's chest is deep and its waist is narrow. The coarse, short fur of the cheetah is tan with round black spots measuring from 2 to 3 cm (0.79 to 1.2 in) across, affording it some camouflage while hunting. There are no spots on its white underside, but the tail has spots, which merge to form four to six dark rings at the end. The tail usually ends in a bushy white tuft. The cheetah has a small head with high-set eyes. Black "tear marks" run from the corner of its eyes down the sides of the nose to its mouth to keep sunlight out of its eyes and to aid in hunting and seeing long distances. Although it can reach high speeds, its body cannot stand long distance running. It is a sprinter.

The adult cheetah weighs from 36 to 65 kg (79 to 140 lb). Its total body length is from 115 to 135 cm (45 to 53 in), while the tail can measure up to 84 cm (33 in) in length. Cheetahs are 67 to 94 cm (26 to 37 in) in high at the shoulder. Males tend to be slightly larger than females and have slightly bigger heads, but there is not a great variation in cheetah sizes and it is difficult to tell males and females apart by appearance alone. Compared to a similarly sized leopard, the cheetah is generally shorter-bodied, but is longer tailed and taller (it averages about 90 cm (35 in) tall) and so it appears more streamlined.

Some cheetahs also have a rare fur pattern mutation: cheetahs with larger, blotchy, merged spots are known as "king cheetahs". It was once thought to be a separate subspecies, but it is merely a mutation of the African cheetah. The "king cheetah" has only been seen in the wild a handful of times, but it has been bred in captivity.

The cheetah's paws have semiretractable claws (known only in three other cat species: the fishing cat, the flat-headed cat and the Iriomote cat), offering extra grip in its high-speed pursuits. The ligament structure of the cheetah's claws is the same as those of other cats; it simply lacks the sheath of skin and fur present in other varieties, and therefore the claws are always visible, with the exception of the dewclaw. The dewclaw itself is much shorter and straighter than that of other cats.

Adaptations that enable the cheetah to run as fast as it does include large nostrils that allow for increased oxygen intake, and an enlarged heart and lungs that work together to circulate oxygen efficiently. During a typical chase, its respiratory rate increases from 60 to 150 breaths per minute. While running, in addition to having good traction due to its semiretractable claws, the cheetah uses its tail as a rudder-like means of steering[citation needed] to allow it to make sharp turns, necessary to outflank prey animals that often make such turns to escape.