多肉植物又被称作肉质植物，是指植物能在气候或土壤干旱的条件下拥有肥大的叶或茎甚至是贮藏器官（例如是根茎），多肉植物主要生长于沙漠及海岸干旱地区。它们的根、茎特别肥大，叶片退化，以利于保存大量的水分。多肉植物主要分布在景天科、龙舌兰科、大戟科、夹竹桃科、百合科、番杏科等。仙人掌亦可算是一种多肉植物，但由于其种类众多，约3000至5000种，加上不是所有仙人掌都是多肉植物，因此大部分的人多半将之独立，例如「仙人掌与多肉植物」或「Cactus and Succulent」。相较于仙人掌科，其他的多肉植物并无「刺座」的组织，部分有硬刺的品种，如大戟科，多半是表皮特化的情形。

In botany, succulent plants, also known as succulents or sometimes fat plants, are plants that have some parts that are more than normally thickened and fleshy, usually to retain water in arid climates or soil conditions. The word "succulent" comes from the Latin word sucus, meaning juice, or sap. Succulent plants may store water in various structures, such as leaves and stems. Some definitions also include roots, so that geophytes that survive unfavorable periods by dying back to underground storage organs may be regarded as succulents. In horticultural use, the term "succulent" is often used in a way which excludes plants that botanists would regard as succulents, such as cacti. Succulents are often grown as ornamental plants because of their striking and unusual appearance.