Apparently there are yams, "yams," and sweet potatoes. Just for fun!yams and sweet potatoes are two completely different things, they are not even related as far as plant species go, but the same rules apply. Or at least I apply the same rules.
Yams are a completely different species and part of the plant from sweet potatoes. They also need to be cooked, but you'll never find one in the US. According to the library of congress website (US), what Americans call "yams" at the grocery store are actually just a different variety of sweet potato.