A yam is a starchy root vegetable that grows underground, similar to a potato but usually much larger. True yams have rough, bark-like skin and white, purple, or reddish flesh inside. They're a major food crop in Africa, Asia, and the Caribbean, where people roast them, boil them, or pound them into a dough-like food.

In the United States, many people call sweet potatoes “yams,” but this is actually a mistake. Real yams and sweet potatoes are completely different plants. Sweet potatoes have smoother skin and orange flesh, while true yams are starchier and less sweet.

If you see canned “yams” at the grocery store, you're almost certainly looking at sweet potatoes. True yams are harder to find in American stores, though you might spot them in international markets. They can grow absolutely huge: some yams weigh over 100 pounds, much larger than any sweet potato you've ever seen.