The term big cat – which is not a biological classification – is used informally to distinguish the larger felid species from smaller ones. One definition of "big cat" includes the four members of the genus Panthera: the tiger, lion, jaguar and leopard. Members of this genus are the only cats able to roar. A more expansive definition of "big cat" also includes the cougar, cheetah, snow leopard and clouded leopard.

Despite enormous differences in size, the various species of cat are quite similar in both structure and behavior, with the exception of the cheetah, which is significantly different from any of the big or 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. (However, neither the snow leopard nor the cheetah can roar, despite having hyoid morphology similar to roaring cats.) 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.