The informal term "big cat" is typically used to refer to any of the four largest (living) members of the entire Panthera genus. Among the five total species within the Panthera genus, these four are the only cats that are able to roar. In descending order of their maximum potential size, these four species are: tigers, lions, jaguars, and leopards. A more liberal and expansive definition is sometimes used which may include the snow leopard, puma, clouded leopard, Sunda clouded leopard and/or cheetah, although these added species do not roar. The two clouded leopard species are considered an evolutionary link between big and small cats.
Despite enormous differences in size, various species of cat are quite similar in both structure and behaviour, with the exception of the cheetah, which significantly stands out from the other big and small cats. All cats are carnivores and efficient apex predators. Their range includes the Americas, Africa, Asia, and Europe.
The ability to roar comes from an elongated and specially adapted larynx and hyoid apparatus. When air passes through the larynx on the way from the lungs, the cartilage walls of the larynx vibrate, producing sound. The lion's larynx is longest, giving it the most robust roar. All five extant members of the Panthera genus contain this elongated hyoid but due to differences in the larynx the snow leopard cannot roar.