Checks
Longitudinal separation of the fibers in wood that do not go through the whole cross section. Checks result from tension stresses during the drying process.

Compressive Strength Parallel to Grain
Maximum stress sustained by a compression parallel-to-grain specimen having a ratio of length to least dimension of less than 11.

Compressive Stress Perpendicular to Grain
Reported as stress at proportional limit. There is no clearly defined ultimate stress for this property.

Density
Weight per unit volume. Density of wood is influenced by rate of growth, percentage of late wood and in individual pieces, the proportion of the heartwood.

Dimensional Stability
A term that describes whether a section of wood will resist changes in volume with variation in moisture content (other term: movement in performance).

Figure
The pattern produced in a wood surface by annual growth rings, rays, knots, deviations from regular grain, such as interlocked and wavy, and irregular colouration.

Grain
The direction, size, arrangement, appearance, or quality of the fibers in sawn wood. Straight grain is used to describe lumber where the fibers and other longitudinal elements run parallel to the axis of the piece.

Growth ring
Layer of wood added to a tree during a single growing season…made up of earlywood and latewood.

No two pieces of hardwood are alike. Because of this, your particular item looks like no other in the world...including those in the showroom. However, rest assured that none of the natural markings that characterize hardwood floors, furniture, woodwork, and cabinetry affect their durability or structural integrity.

http://en.wikipedia.org/wiki/Growth_rings

Gum Pocket
An excessive local accumulation of resin or gum in the wood.

Hardness
Generally defined as resistance to indentation using a modified Janka hardness test, measured by the load required to embed a 11.28 mm (0.444 in.) ball to one-half its diameter. Values presented are the average of radial and tangential penetrations.

Hardwood
A description applied to woods from deciduous broad-leafed trees (Angiosperms). The term has no reference to the actual hardness of the wood.

Heartwood
The inner layers of wood in growing trees that have ceased to contain living cells. Heartwood is generally darker than sapwood, but the two are not always clearly differentiated.

Impact Bending
In the impact bending test, a hammer of given weight is dropped upon a beam from successively increased heights until rupture occurs or the beam deflects 152 mm (6 in.) or more. The height of the maximum drop, or the drop that causes failure, is a comparative value that represents the ability of wood to absorb shocks that cause stress beyond the proportional limit.

Knots
Hard, cylindrical regions marking locations of branches that have been encased by later growth of the tree.

Mineral Stain
Olive or grayish markings caused by such environmental factors as trace elements in water or soil.

Modulus of Elasticity
An imaginary stress necessary to stretch a piece of material to twice its length or compress it to half its length. Values for the individual species are given in megapascals (MPa - equivalent to N/m2), and are based on testing small clear pieces of dry wood.

Modulus of Rupture
Reflects the maximum load-carrying capacity of a member in bending, and is proportional to maximum moment borne by the specimen. Modulus of rupture is an accepted criterion of strength, although it is not a true stress because the formula by which it is computed is valid only to the elastic limit.

Moisture Content (M.C.)
The weight of water contained in wood expressed as a percentage of the weight of the oven dry wood.

Pith Flecks
Pith-like irregular discoloured streaks of tissue in wood, due to insect attack on the growing tree.

Plain-Sawn
Plain-sawn hardwood boards are produced by cutting tangentially to a tree’s growth rings, creating the familiar “flame-shaped” or “cathedral” pattern. This method also produces the most lumber from each log, making plain-sawn lumber a cost effective design choice.

Plain-sawn lumber will expand and contract more than boards sawn by other methods. However, it performs just as well when properly kiln-dried, when the job site is properly prepared and when the hardwood products are acclimated to the home before installation. (See Managing Expansion & Contraction, Moisture Content)

Quarter-Sawn
Quarter-sawing means cutting a log radially (90-degree angle) to the growth rings to produce a “vertical” and uniform pattern grain. This method yields fewer and narrower boards per log than plain sawing, boosting their cost significantly. Quarter-sawn boards are popular for decorative applications such as cabinet faces or wainscoting. They will expand and contract less than boards sawn by other methods.

Rift-Sawn
Rift-sawing at a 30-degree or greater angle to the growth rings produces narrow boards with accentuated vertical or “straight” grain patterns. Rift-sawn boards are often favored for fine furniture and other applications where matching grain is important. This type of lumber is available in limited quantities and species.

Sapwood
The outer zone of wood in a tree, next to the bark. Sapwood is generally lighter than heartwood.

Sapwood Colour
The paler-coloured wood closer to the bark of the tree.

Shear Strength Parallel to Grain
Ability to resist internal slipping of one part upon another along the grain. Values presented are average strength in radial and tangential shear planes.

Shrinkage
The contraction of wood fibers caused by drying below the fiber saturation point (usually around 25-27% M.C.). Values are expressed as a percentage of the dimension of the wood when green.

Specific Gravity
The relative weight of a substance compared with that of an equal volume of water. The S.G. of wood is usually based on the green volume and oven dry weight.

Split
Separation of the fibers in a piece of wood from face to face (other term: end-split).

Stain
Materials used to impart colour to wood.

Tensile Strength Perpendicular to Grain
Resistance of wood to forces acting across the grain that tend to split a member. Values presented are the average of radial and tangential observations.

Texture
Determined by relative size and distribution of the wood elements. Described as coarse (large elements), fine (small elements) or even (uniform size of elements).

Warp
Distortion in lumber causing departure from its original plane, usually developed during drying. Warp includes cup, bow, crook and twist.

Weight
The weight of dry wood depends upon the cellular space, the proportion of wood substance to air space.

Work to Maximum Load in Bending
Ability to absorb shock with some permanent deformation and more or less injury to a specimen. Work to maximum load is a measure of the combined strength and toughness of wood under bending stresses.