Yam is the common name for members of the genus Dioscorea. Some species are cultivated for consumption in Africa and Asia. The word "yam" is from the West African nyami, meaning "to eat". They are used in a similar fashion to potatoes, and are sometimes called a potato substitute, though in those areas where yams are grown, potatoes are the newer vegetable.
The sweeter varieties of sweet potato (Ipomoea) are often called "yams", causing much confusion.