Vivipara is a term used to describe organisms that give birth to live young, as opposed to laying eggs. There are several synonyms for vivipara, including ovovivipara, matrotrophic, and placental. Ovovivipara refers to organisms that produce eggs that hatch within the body, while matrotrophic organisms rely on nutrient transfer from the mother to the developing young. Placental is used to describe a specific type of viviparity in mammals, where a placenta attaches to the uterine wall and provides nutrients and oxygen to the developing fetus. Each of these terms describes a different aspect of viviparity and is useful for categorizing and understanding different species' reproductive strategies.