The term heartwood is a part of a tree's anatomy. It is the innermost layer of wood in a tree, and is usually darker in color than the outer sapwood. The term duramen is another name for heartwood, and is derived from the Latin word for 'HARD'. Duramen is also known as heartwood because it is the hardest and densest part of the tree. Heartwood is important for providing structural support to the tree, and is also resistant to decay.