When yam is used as medicine, it is called Huai Yam, which is called Huai Shan for short. Huai comes from a place name, and there are many names, such as Tushu, Shanshu, Dioscorea opposita, and Yuyan Potato. Sweet potato is a kind of potato, so it is called sweet potato because its skin is mostly red. The scientific name of potato is Maling Potato. Because it tastes like potato when cooked, some places in southern Jiangsu and Zhejiang provinces are also called foreign sweet potato.