The terms sweet potato vs yam are used interchangeably on canned ingredients in cooking and at the grocery stores. But they are totally different roots. The sweet potato is in the morning glory family and the yam is in the lily family.
Sweet potatoes can be grown in our gardens (along with some patience). There are two kinds: one being a yellow and light orange flesh with a dry texture. The other is the darker varieties of deeper orange and red color which are sweet and moist. Varieties you can plant are Georgia Jet, Centennial, and Puerto Rico.
The basic sweet potato comes from Central and South America imported to the southern United States. The African slaves grew them because of the high productivity from small gardens. Being cheap to grow, they incorporated sweet potatoes in most dishes including my favorite sweet potato pie. So, they substituted sweet potatoes for the African yams they knew about.
Yams grow in the tropics of Africa and later grown in the Caribbean and Asia. Yam is a vining plant producing white or light-yellow flesh. Some yams can weigh over 150 pounds.
The African culture began calling the sweet potato a yam because that is what reminded them of. That is where the confusion comes from.