A yam is the tuber of a vine, found in many countries around the world. Yam tubers can grow very big - up to 70kg. Yams have a rough skin that is hard to peel, but much softer flesh inside.
Many people call sweet potatoes yams or sweet yams, but they are actually different vegetables.
Some variety of yam can be eaten raw, but most need to be cooked. Yams can be fried, boiled, pounded down and made into a dough. They can also be dried and powdered and used to make something similar to instant mashed potato.
A yawn is where your mouth opens wide and you take a deep breath in and out. Yawns just happen by themselves, they are hard to stop.
People and animals yawn when they are tired, stressed, overworked or bored, or for no reason at all. Yawning is infectious - if someone near you yawns, you often start yawning too! You might even start to yawn by looking at a photo of someone yawning, so don't stare at the photo of the yawning cat for too long.