A knar is a knot on a tree that is formed when a branch grows around another branch or the trunk of the tree. A GNARL is a knot on a tree that is caused by the twisting and bending of the wood fibers. A BURL is a knot on a tree that is caused by a fungal infection, which causes the wood to swell and form a lumpy growth. All three of these knots are common on trees and can be found in many different types of wood.