胎生可用来形容一些动物与植物的繁衍方式，但两者的定义并 不直接相关。

以动物来说，胎生是指受精卵在母体的子宫内发育为胎儿产出母体。胚胎通过诸如卵黄囊及胎盘等结构自母体获得 营养，直至出生时为止。

哺乳类动物如猴、虎、牛、羊等，都是胎生，蓝鲸是世界上最大的胎生动物。有一些毒蛇（如蝮蛇、海蛇）介于卵生和胎生之间，发育期间营养则由蛋黄提供，被称为卵胎生。

以植物来说，则是指种子成熟后还未脱离母株即在子房（果实）内发芽的现象，芽苗生长到一定程度后才脱离母株。和动物胎生不同的是，这里的种子并不靠母株供给营养，而是以种子内胚乳所储藏的营养来发育。

Viviparity literally means "giving live birth", from the Latin vivus ("living") and parere ("to beget"). The term is in use both in zoology and in botany as a term for certain classes of modes of reproduction, though it has different meanings in the two contexts.
The adjective viviparous is derived from "viviparity" and describes both the various modes of reproduction and the organisms that reproduce in any such mode.