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.