Possums are arboreal marsupials indigenous to Australia and New Guinea. They are different animals than the North American opossum, which is sometimes also called a possum.
There are approximately 70 species of possum, most of which live in trees for at least part of their lives and are nocturnal. Possums are also mostly herbivorous, although several species are insectivorous or nectivorous. Like kangaroos, possums give birth to underdeveloped young that live in the mother's pouch.
The common brushtail possum is an invasive species in New Zealand due to its introduction for purposes of the fur trade. Brushtail possums have no predators in New Zealand and are destructive to native flora and fauna. They also negatively impact agriculture by transmitting bovine tuberculosis.
Some people use the term possum to refer to the Virginia opossum, native to North America. Like possums, the Virginia opossum is a marsupial, but they are not closely related and actually belong to two different taxonomic orders. Like possums, the Virginia opossum is nocturnal and adept at climbing trees. However, it is an opportunistic omnivore, feeding on fruit, insects and meat. Opossums frequently scavenge for carrion and, in human-populated areas, often raid garbage cans. Aside from scavenging, opossums also catch and kill snakes and are somewhat resistant to venom.