A feral pig is a domestic pig which has gone feral, meaning it lives in the wild. The term feral pig has also been applied to wild boars, which can interbreed with domestic pigs. They are found mostly in the Americas and Australia. Razorback and wild hog are Americanisms applied to feral pigs or boar–pig hybrids.

The pig, also called swine or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus Sus. It is considered a subspecies of Sus scrofa by some authorities, but as a distinct species by others. Pigs were domesticated in the Neolithic, both in East Asia and in the Near East. When domesticated pigs arrived in Europe, they extensively interbred with wild boar but retained their domesticated features.