The word "rhinoceros" comes from Ancient Greek ῥινόκερως (rhinókerōs), meaning 'nose-horned', from ῥίς (rhis) 'nose' and κέρας (kéras) 'horn'.
A rhinoceros, commonly abbreviated to rhino, is a member of any of the five extant or numerous extinct species of odd-toed ungulates (perissodactyls) in the family Rhinocerotidae. Two of the living species are native to Africa, and three to South and Southeast Asia.
Rhinoceroses are among the largest remaining megafauna, each weighing over half a tonne in adulthood. They are herbivorous, have relatively small brains (400–600 g), one or two horns, and a thick, protective skin 1.5–5 cm in thickness, made from collagen in a lattice structure.
They mostly consume leafy vegetation, but can digest fibrous plant matter thanks to hindgut fermentation. Unlike other perissodactyls, the African species lack front teeth, using their lips to gather food.
Rhinoceroses are heavily poached for their horns, which are traded on the black market at high prices. Most living species are endangered due to this demand, driven largely by markets in China and Vietnam, where rhino horn is used in traditional medicine despite a lack of scientific evidence for its efficacy.
Rhino horns, made of keratin (the same substance as human hair and nails), are also used for dagger handles in Yemen—a major demand driver in the 1970s and 1980s.