In Australia, any young animal can be called a joey, although the term is usually employed in discussions of marsupials, and most specifically kangaroos. A baby kangaroo is considered a joey until it reaches fully independent adulthood, which can take up to one year after birth. When used outside of Australia, most people understand a joey to mean a young kangaroo.
Kangaroos have an interesting reproductive cycle. The joey is actually born in an embryonic state and is forced to crawl up its mother and into her pouch to nurse. The joey attaches so firmly to the pouch that attempts to remove it could kill the joey and damage the mother's nipples. Over the next eight to 10 months, the joey develops into a recognizable baby kangaroo, and after around eight months, it begins to climb out of the pouch to investigate the world, always staying close to mother and continuing to nurse until it is a year old.
The mother kangaroo, or flyer, is capable of contracting the muscles of the pouch to keep the joey safely tucked in while she is in motion, or releasing the muscles to let the joey out. The mother kangaroo regularly cleans the pouch, cleaning around the joey when it is very young and tipping it out for cleaning when it is older. One of the more curious aspects of the kangaroo's mating cycle is that the female mates again within a few days of giving birth, but the resulting embryo is put into a state of stasis. If the joey dies, the embryo will develop into a new joey: otherwise, the embryo will remain in embryonic diapause for up to a year, waiting for the pouch to become available.
Kangaroos are perhaps the most famous Australian animal, and there are over 40 known species ranging from small wallabies to giant red kangaroos. The large and curious herbivores have experienced clashes with humans, as they are destructive for both gardens and fences, although some Australians do keep kangaroos as pets, usually obtaining them as very young joeys so that they will be tamable. Raising a joey can be difficult for the inexperienced, as they have special dietary needs and also need to be kept warm and secure. Most wildlife authorities in Australia recommend that a joey be taken to a wildlife center for care if found without a parent, and people interested in keeping them as pets should get permits, as they are illegal without a license.