The common walnut trees are called Persian walnut as well. The official name is Juglans regia.
Walnuts are fruit, even though we call them nuts. The nuts themselves are called seeds.
Walnuts are used in salads and for sweets. They are popular in the US and have a distinct flavor. The nut itself is soft, not crunchy.
All the pictures are from Wikimedia Commons.
This is a common walnut tree in Desvojca, Kosovo by, User: Durim shkodra.