The kangaroo is a marsupial from the family Macropodidae (macropods, meaning “large foot”). In common use the term is used to describe the largest species from this family, especially those of the genus Macropus: the red kangaroo, antilopine kangaroo, eastern grey kangaroo, and western grey kangaroo. Kangaroos are endemic to Australia.
As with the terms “wallaroo” and “wallaby”, “kangaroo” refers to a polyphyletic grouping of species. They are distinguished according to size. The largest species in the family are called “kangaroos” and the smallest are generally called “wallabies”. The term “wallaroos” refers to species of an intermediate size.
The large kangaroos have adapted much better than the smaller macropods to land clearing for pastoral agriculture and habitat changes brought to the Australian landscape by humans. Many of the smaller species are rare and endangered, while kangaroos are relatively plentiful.
More information on Kangaroos can be found on Wikipedia.