A cockatoo is any of the 21 bird species belonging to the family Cacatuidae. Along with the Psittacidae family (the true parrots), they make up the order Psittaciformes. The name cockatoo originated from the Malay name for these birds, kakaktua, which translates literally as older sister (from kakak, "sister," and tua, "old")
Cockatoos share many features with other parrots including the characteristic curved beak shape and a zygodactyl foot, with two forward toes and two backwards toes. They differ, however in a number of characteristics, including the often spectacular movable headcrest, the presence of a gall bladder and some other anatomical details, and their lack of the Dyck texture feather composition which causes the bright blues and greens seen in true parrots. Cockatoo species are also, on average, larger than the true parrots (however, the cockatiel is a small cockatoo and the very large parrots include the Hyacinth Macaw by length and the Kakapo by weight.)
Cockatoos have a much more restricted range than the true parrots, occurring naturally only in Australia and nearby islands. Eleven of the 21 species exist in the wild only in Australia, while seven species occur in Indonesia, New Guinea, and other south Pacific islands. Three species occur in both New Guinea and Australia.