动物是多细胞真核生命体中的一大类群，统称为动物界。动物身体的基本形态会随着其发育而变得固定，通常是在其胚胎发育时，但也有些动物会在其生命中有变态的过程。

绝大多数动物都是能够自发且独立地移动的探索者，只有极少数的动物是固定在一点无法移动。珊瑚便是其中一种无法移动的「动物」，但由于牠们能够伸出触手来捕食的关系，所以也被归类为动物；亚里士多德最初称这种生物为「zoophyta」，意思是介乎植物与动物之间的生物，后来古波斯学者比鲁尼在公元十世纪时建议将牠们归类为动物，但一直要等到十八世纪牠们才正式并入动物界。

Animals are multicellular, eukaryotic organisms of the kingdom Animalia (also called Metazoa). All animals are motile, meaning they can move spontaneously and independently, at some point in their lives. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their lives. All animals are heterotrophs: they must ingest other organisms or their products for sustenance.