Yams are confusing.
Or at least the word is.
The "true yam" is a starchy tuber that I associate with Africa. It can grow up to eight feet long, and can weigh up to 150 pounds (says Wikipedia). I gather that the flavor is kind of bland, but I've never eaten one; I don't think I've ever even seen one.
But in much of the US, when people refer to "yams," what they're talking about is a rather different starchy tuber. When trying to make clear that they're not talking about the true yam, some people note that they're referring to sweet potatoes.
But that, too, is confusing, because there are at least two prominent kinds of sweet potatoes. One kind looks pretty much like an ordinary brown-skinned potato, and has pale yellowish flesh, and if I remember right is barely sweet at all. The other kind is longer and thinner and knobblier and has redder skin than an ordinary potato, and tapers to a point at each end, and has deep orange flesh, and tastes quite sweet when baked. I like them a lot, though given how sweet and yummy they are, I don't understand the common penchant for candying them by adding sugar and marshmallows and stuff.
If I'm understanding right, both of those kinds of sweet potato are the same species, just different variants. But their flavor and look is very different, so I'm never quite sure what I'm in for when someone tells me they're going to cook some sweet potatoes.
But I suppose if they instead mention "yams," the ambiguity is even stronger. Not only might they be talking about African true yams, they might be referring to such other items as: the Ugaritic god Yam; a Pony Express-like messenger system developed by the Mongols; oca (the "New Zealand yam"); or the Saudi Arabian tribe known as the Banu Yam.
And doesn't that sound like a set of made-up Fictionary definitions?