鳖是龟鳖目鳖科（学名：Trionychidae）软壳水生龟的统称，又名甲鱼、水鱼、泥龟、王八，共有20多种。中国现存主要有中华鳖、山瑞鳖、斑鳖、鼋，其中以中华鳖最为常见。

主要分布于亚洲、非洲、美洲的淡水和湖泊之中。

The Trionychidae are a taxonomic family of a number of turtle genera commonly known as softshells. They are also sometimes called pancake turtles (although they are distinct from the pancake tortoise). Softshells include some of the world's largest freshwater turtles, though many can adapt to living in highly brackish areas. Members of this family occur in Africa, Asia, and North America. North American members of genus Trionyx were fairly recently (1987) assigned the resurrected genus name Apalone by Meylan, though they are still listed semicorrectly as Trionyx in some texts.