African slaves who came to the US called the local sweet potato “nyami,” which translates to “yam” in English. This is because it reminded them of true yams, a food staple they knew in Africa. In addition, the darker-skinned, orange-fleshed sweet potato variety was only introduced to the US several decades ago. In order to set it apart from paler-skinned sweet potatoes, producers labeled them “yams.” —healthline.com