What's the difference between Wallaby and Joey?

'Joey' is the general term for young wallabies and kangaroos. Kinda like 'puppies.'

A joey is a baby marsupial of any description,  whether a macropod, a koala, a possum or a wombat. A wallaby is one of a number of macropod species smaller than a kangaroo but bigger than a euro. A joey kangaroo that is almost ready to leave the pouch permanently can be bigger than several species of fully grown wallaby.