| A | B |
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| Actual dimension | true dimension of a material, as distinct from its nominal dimension. |
| AFPA | American Forest Products Association; association that grades lumber. |
| Air drying | Seasoning wood in the open air. |
| Alkaline copper quat (ACQ) | A chemical used to preserve wood against attack by decay and insects. |
| Annual rings | Smaller rings inside the bark that move toward the center of the trunk. A new ring is typically added every year. |
| Appearance grading | The grading of wood for its appearance properties, as distinct from its structural properties; not to be confused with visual grading. |
| AWPA | American Wood Preservative Association |
| Bark | The external covering of the woody stems, branches, and roots of the plants, as distinct and separable from the wood itself. |
| Board foot | The amount of lumber contained in a nominal 1-in.-thick board that measures 12 in x 12 inches (nominal) |
| Board | A piece of wood sawed thin and of considerable length and breadth compared with the thickness. |
| Bound water | The cell wall water. In wood, the water held within the cellulose of the cell walls. |
| Brown rot | Term used for the form of decay caused by a type of fungus that consumes cellulose (white in color) and makes wood turn more brown. |
| Cambium | The layer that lies between the bark and the outermost growth ring. The cells of this layer divide and subdivide, producing the cells of the growth rings and the bark. The thin layer beneath the bark of a tree that manufactures cells of wood and bark. |
| Cellulose | A complex polymeric carbohydrate of which the structural fibers in wood are composed. |
| Check | A separation of wood fibers along the rays (perpendicular to the growth rings). Distortion in the wood usually caused by shrinkage stresses. |
| Chromate copper arsenate (CCA) | A waterborne mixture of the compounds of copper, chromium, and arsenic. A chemical used to protect wood against attack by decay and insects. Due to toxicity concerns, this chemical has been phased out of most treated wood used in residential and commercial building construction. |
| Creosote | An oily liquid having a burning taste and a penetrating odor, obtained by the distillation of coal and wood tar, used mainly as a preservative for wood and as an antiseptic. |
| Cup | A curl in the cross section of a board or timber caused by unequal shrinkage or expansion between one side of the board and the other. |
| Dimensional lumber | Lengths of wood, rectangular in cross section, sawed directly from the log. |
| Dry lumber | A piece of lumber whose moisture content is less than or equal to 19%. |
| Earlywood | Cells (lighter) added during the wet season. |
| Encased knot | A knot that is not loose, but tightly intergrown with the adjoining tissue. |
| End tag | A plastic tag stapled to an end of a treated lumber member that carries the treater’s stamp. |
| Equilibrium moisture content (EMC) | The moisture content at which wood stabilizes after a period of time in its destination environment. |
| Fiber saturation point (FSP) | The stage at which all the free water has evaporated and the bound water has just begun to evaporate. |
| Fiber | Small diameter-gives the tree structural strength. |
| Fire-retardant treatment (FRT) | Accomplished by placing lumber in a vessel and impregnating it under pressure with certain chemical salts that greatly reduces its combustibility. |
| Flat sawing | To reduce a squared log to boards with evenly spaced parallel cuts, causing less waste of timber. |
| Flat sawn lumber | Lumber produced by sawing a log in one or two directions only. The grain pattern varies from nearly parallel to the wide face to perpendicular. |
| Flat-grain | Dimension lumber sawed in such a way that the annual rings are oriented close to parallel with the face. |
| Forest Stewardship Council (FSC) | The most widely recognized wood certifying body. |
| Free water | The cavity water. In wood, water held with the cavities of the cells. |
| Fungal decay | Deterioration of wood caused by fungi. |
| Grading rules – writing agencies | Seven agencies in North America (6 in the U.S. and 1 in Canada) that prescribe grading rules and also function as inspection agencies |
| Grain | In wood, the direction of the longitudinal axes of the wood fibers or the figure formed by the fibers. |
| Green lumber | A piece of lumber whose moisture content is 20% or greater. Unseasoned lumber. |
| Growth ring | A nearly circular ring of wood fibers; a tree adds approximately one ring per year. |
| Hardwood | Wood obtained from trees that are deciduous and have board leaves. Wood from deciduous (broadleaf) trees. |
| Heartwood | The central portion of a tree trunk that no longer conducts nutrients, generally darker than sapwood. The dead wood cells in the center region of a tree trunk. |
| Insect damage | Damage that occurred during the life of the tree that may or may not affect the usual properties of the piece of lumber, depending on whether the organisms are still alive in the wood and the extent of the damage. |
| KD | Identification on wood that stands for kiln dried. |
| KDAT | Kiln dried after treatment; stamped on a piece of lumber kiln dried to less than or equal to 19% moisture content after treatment. |
| Knot | An approximately circular formation of wood fibers formed where a limb branches from a tree trunk. A knot generally lowers the strength of wood. A growth characteristic in wood, occurring where a branch joins the trunk of the tree from which the wood has been sawed. |
| Latewood | Cells (denser) added during the dry season. |
| Lignin | The natural cementing substance that binds together the cellulose in wood. |
| Longitudinal shrinkage | In wood, shrinkage along the length of the log. |
| Loose knot | Results when the branch dies during the tree’s growth and the successive growth rings of the trunk encircle this dead branch. |
| Lumber | Solid wood products derived directly from logs by sawing and planing only, with no additional machining. Timber sawed or split into planks, boards, etc. |
| Machine grading | A method of grading lumber using a machine, also called machine stress-rated lumber (MSR), in contrast with the more commonly used method of visual grading. The grading of wood for its structural properties, performed by automated machinery, as distinct from visual grading. |
| Machine stress-rated (MSR) lumber or machine-rated lumber | A method of grading lumber using a machine. |
| Manufacturing characteristics | Discontinuities in the structure of the wood that were created at the mill. |
| Nominal dimension | An approximate dimension assigned to a piece of material as a convenience in referring to the piece. |
| Photosynthesis | The process in which water and the environment react with carbon dioxide in the air to produce a basic sugar (glucose), releasing oxygen. This reaction requires a tree or plant as the medium and the presence of light energy from the sun. |
| Plainsawn, flatsawn | Sawing a log into dimension lumber without regard to the direction of the annual rings. |
| Preservative-treated wood | Wood that has been impregnated with preservative chemicals to increase its resistance to decay and biological attack; also commonly called pressure-treated wood. |
| Pressure impregnation | Preservative chemicals that are deeply driven into the fibers of wood. |
| Pressure-treated wood/lumber | Wood into which preservatives have been pressure injected to retard termite infestation and fungal decay. Using a different preservative, the pressure treatment can also be used for increasing the fire resistance of wood. Wood that has been impregnated with chemicals under pressure for the purpose of retarding decay or reducing combustibility. |
| Quartersawn, riftsawn, edge-sawn | Lumber sawn in a way that the annual rings run roughly perpendicular to the faces of each piece. |
| Radial shrinkage | In wood, shrinkage perpendicular to the growth rings. |
| Radial-sawn lumber | Lumber that is produced from first converting the log into four pieces through the center. |
| Reclaimed lumber | Wood obtained from demolishing old barns, mills, and factories. |
| S1S | Surfaced on one side. |
| S1S1E | Surfaced on one side and one edge. |
| S2S | Surfaced on two sides. |
| S4S | Surfaced on all four sides. |
| Sap | Term for the food that the tree conducts. |
| Sapwood | The outer portion of a tree trunk that conducts nutrients, typically lighter in color than heartwood. The living wood in the outer region of a tree trunk or branch. |
| Sawn lumber | Lumber which has been sawn from logs as opposed to lumber that has been reprocessed. |
| Sawyer | A person who saws wood, esp. as an occupation. |
| S-DRY | Designation in a lumber grade stamp that indicates that the wood was surfaced (planed) when in a seasoned (dry) condition. |
| Seasoned | (seasoning) The drying of wood, to bring its moisture content into equilibrium, with ambient conditions.Process of drying of lumber until the moisture content reaches the desired percentage. |
| S-GRN | Designation in a lumber grade stamp that indicates that the wood was planed when green. |
| Shake | A separation of wood fibers along the growth rings. |
| Softwood | Wood obtained from trees that have thin conical leaves and are typically evergreen. Wood from coniferous (evergreen) trees. |
| Solid lumber | Lumber which has been sawn from logs as opposed to lumber that has been reprocessed. |
| Solid sawn lumber | Lumber which has been sawn from logs as opposed to lumber that has been reprocessed. |
| Split | A complete separation of wood fibers through the entire end of a member. To divide or separate from end to end or into layers. |
| Springwood, earlywood | In wood, the portion of the growth ring comprised of relatively larger, less dense cells; also called earlywood. |
| Sticker | Small pieces of wood placed in between to keep the boards separated for ventilation during air drying. |
| Structural insulated panel (SIP) | Structural panels composed of rigid insulation glued on each side with oriented strandboard or plywood panels. |
| Summerwood, latewood | In wood, the portion of the growth ring compromised of relatively smaller, denser cells; also called latewood. |
| Surfaced | (surfacing) Smoothing the surface of a material, usually by planing. Process of smoothing lumber, rounding off the edges, and making it more square, removing some of the distortions that have occurred during the seasoning process. |
| Sustainable Forestry Initiative (SFI) | Another wood certifying organization. |
| Tangential shrinkage | In wood, shrinkage along the circumference of the log. |
| Timber | Standing trees; a large piece of dimension lumber. |
| Visual grading | A method of grading lumber based in visual inspection of each piece by trained (graders) inspectors. The grading of wood for its structural properties, based on visual inspection, as distinct from machine grading; not to be confused with appearance grading. |
| Wane | The absence of wood or the presence of bark at the corner or the edge of a piece that results from the sawing process. An irregular rounding of a long edge of a piece of dimension lumber caused by cutting the lumber from too near the outside surface of the log. |
