The scientific term for an animal that lays eggs is oviparous. The word comes from the Latin words "ova," meaning egg, and "parous," meaning bearing or producing. Animals that produce live young are called "viviparous."
Egg laying is common to all species of birds and most reptiles, though several species of snakes and lizards are viviparous. Most fish and amphibians are oviparous as well. Among mammals, only the platypus and four species of echidna lay eggs. There is a third mode of reproduction, called "ovovivipary" in which embryos develop inside eggs that are held within the mother's body, until they are ready to hatch.