Possums and opossums are both medium-sized marsupials. While sometimes opossums are called possums for short, the two groups live on different continents, are not closely related, and have very different teeth and paws. Opossums are native to North and South America, while possums are from Australia and surrounding islands.
Opossums are a very old group, with features that are similar to early mammals. They have five toes on each foot and canine teeth, and they are usually omnivorous. Few are strict herbivores, and some even hunt venomous snakes. They can be found throughout the Americas, but the most well-known species is probably the Virginia opossum, the only species native to the United States.
Possums, in contrast, live in Australia, are related to kangaroos and koalas, and have some unique adaptations that make them very distinct from early mammals. All animals in Diprotodontia, possums included, have fused toes on their hind feet, lack canine teeth entirely, and have specialized incisors in their lower jaw. Their odd incisors are specifically adapted for eating plants. The most common possum in Australia, the brushtail, is somewhat unusual among the group Diprotodontia in that it also eats eggs and small prey.