Viviparity has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs. In plants, where the term vivipary is more usual, it means reproduction via embryos, such as buds, that develop from the outset without interruption, as opposed to germinating externally from a seed. In both animals and plants, the adjective viviparous is used to describe the condition.
Five modes of reproduction can be differentiated in animals based on relations between zygote and parents, including two nonviviparous modes: ovuliparity, with external fertilisation, and oviparity, with internal fertilisation. In the latter, the female lays zygotes as eggs with a large yolk; this occurs in all birds, most reptiles, and some fishes. These modes are distinguished from viviparity, which covers all the modes that result in live birth: