A common misconception is that sweet potatoes and yams are the same thing. It is very amusing when it causes a polite disagreement at the supper table which then degrades to a slightly louder and less polite dissent, followed by an all out food fight. (I do recommend that at these times, just sit back in your chair and watch, never ever get involved, always record the evidence)
So talking to a friend about food, naturally, her mother says “pass the yams” to a sibling. The sibling, a teacher, politely dissents that the bowl of mashed orange stuff on the table are in fact sweet potato. The conversation rapidly degrades into name calling and eventually flung “yam”.
So. What IS the difference, and why is everyone so very confused?