What is "marsupial"?

Marsupial is a type of mammal that is characterized by giving birth to relatively undeveloped young, which continue to develop outside of the womb in a pouch called a marsupium which is a defining feature of marsupials, as is their unique reproductive system. Unlike placental mammals, marsupials have a bifurcated reproductive tract, which separates the urinary, fecal, and reproductive systems. They are found mainly in Australia and nearby islands, but also in the Americas, where they include species such as opossums, shrew opossums, and the extinct thylacosmilids. Examples of marsupials include kangaroos, wallabies, and opossums. They are primarily found in Australia, but can also be found in the Americas.