肢，或称肢体，是指动物的手和脚。哺乳类动物拥有四条肢体，故又称为四肢。另一方面，手臂和腿也分别可称为上肢和下肢。昆虫的肢体则多很多，如毛虫、蜈蚣有很多附肢。

In invertebrate biology, an appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body (in vertebrate biology, an example would be a vertebrate's limbs). It is a general term that covers any of the homologous body parts that may extend from a body segment. These include antennae, mouthparts (including mandibles, maxillae and maxillipeds), gills, walking legs (pereiopods), swimming legs (pleopods), sexual organs (gonopods), and parts of the tail (uropods). Typically, each body segment carries one pair of appendages.