Felidae is the biological family of the cats; a member of this family is called a felid. The most familiar felid is the domestic cat, which first became associated with humans about 10,000 years ago; but the family includes all other wild cats, including the big cats.
Extant felids belong to one of two subfamilies: Pantherinae (which includes the tiger, the lion, the jaguar, and the leopard), and Felinae (which includes the cougar, the cheetah, the lynxes, the ocelot, and the domestic cat).
The first felids emerged during the Oligocene, about 25 million years ago. In prehistoric times, a third subfamily, known as Machairodontinae, included the "saber-toothed cats", such as the well known Smilodon. Other superficially cat-like mammals, such as the marsupial sabertooth Thylacosmilus or the Nimravidae, are not included in Felidae despite superficial similarities.
Felids are the strictest carnivores of the 13 terrestrial families in the order Carnivora, although the three families of marine mammals comprising the superfamily Pinnipedia are as carnivorous as the felids.[source]