Definition: Yams vs. Sweet Potatoes

What's the difference between a yam and a sweet potato?

Apparently, they're not even related according to this Huffington Post article!
And apparently, the U.S. government has perpetuated this confusion.  Here is a summary of the differences:

Sweet Potatoes

• Come in 2 varieties here in the U.S.  One has a golden skin with creamy white flesh and crumbly texture; the other has a copper skin with orange flesh that is sweet and soft.
• All are basically the same shape and size with tapered ends; they're generally much smaller than yams.
• The USDA labels the orange-fleshed ones as "yams" to distinguish them from the white fleshed variety even though they're not really yams!

Yams

• There are many varieties, but most have black bark-like skin and white, purple or reddish flesh.
• BTW, did you know that the word yam comes from an African word meaning "to eat?"

After reading the article, I've realized that I may have never had a yam . . .