Got Wood? Domestic Wood Turning Blanks Glossary of Log Terminology, Part 1

Log Terminology, Part 1 - The Tree Exterior
Burl/Burr/Bur A bulbous formation occasionally found both on the trunks of trees and in the root systems as well. Typically, these formations are caused by stresses - fungal infections, insect infestations, embedded foreign objects and many other things as well. An annular ring burl is simply an area of the tree which is growing at an accelerated rate, displaying very little figure and color. Other burls, such as cluster burls (found on the tree trunk) or root burls (found in the roots) are formed from tightly grouped dormant buds which continue to form (but not grow), producing striking patterns when sawn. The latter form of burl is much sought after by wood turners.
Crotch The "crotch" of a tree refers to the area where two or more branches intersect. Many times, bark will form well into the inner part of the tree, where the two branches grew together over time. These crotches typically show a thick ridge of bark running through the middle of the tree where the branches meet. Sometimes, however, the wood will graft itself together without the formation of bark, producing beautiful grain patterns known as crotchwood feathering, which is explained in the next tutorial.
Healing Growth Healing growth occurs around any type of "wound" that a tree has incurred. This growth can sometimes look very similar to a small burl, but rarely has interesting grain patterns within. Many times these growths will contain voids within and/or bark inclusions.