Lumber is wood that has been processed into uniform and useful sizes, including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing. Lumber has many uses beyond home building. Lumber is referred to as timber in the United Kingdom, Europe, Australia, and New Zealand, while in other parts of the world the term timber refers specifically to unprocessed wood fiber, such as cut logs or standing trees that have yet to be cut.
Wood cut from Victorian Eucalyptus regnans
The harbor of Bellingham, Washington, filled with logs, 1972
A sawmill with the floating logs in Kotka, Finland
A common 50 by 100 mm (2-by-4-inch) board
Wood is a structural tissue found in the stems and roots of trees and other woody plants. It is an organic material – a natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin that resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or more broadly to include the same type of tissue elsewhere, such as in the roots of trees or shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients between the leaves, other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, woodchips, or fiber.
A knot on a tree trunk
Wood knot in vertical section
A section of a yew branch showing 27 annual growth rings, pale sapwood, dark heartwood, and pith (center dark spot). The dark radial lines are small knots.
Cross-section of an oak log showing growth rings