Viviparous animals are animals that give birth to offspring that have developed inside the female reproductive system. The term "viviparity" comes from the Latin words "vivus" meaning "living" and "pario" meaning "give birth to". Here are some key points about viviparous animals:

• Embryo development takes place inside the female reproductive system.
• The embryo obtains nutrients directly from the mother and not from the yolk.
• Once the fetus development is complete, the mother delivers the baby.
• Examples of viviparous animals include humans, dogs, cats, elephants, whales, dolphins, tigers, and kangaroos.

In contrast, oviparous animals lay eggs that hatch externally from the mother. Examples of oviparous animals include birds, lizards, frogs, chickens, alligators, snakes, salamanders, crocodiles, and fishes.

There is also a third category of animals called ovoviviparous animals. In these animals, the eggs develop inside the females body, but the embryo obtains nutrients from the yolk sac and not directly from the mother. Examples of ovoviviparous animals include sharks, rays, snakes, fishes, and insects.

In summary, viviparous animals are those that give birth to offspring that have developed inside the female reproductive system. Examples include humans, dogs, cats, elephants, whales, dolphins, tigers, and kangaroos.