Heartwood
The inner, older wood in a tree that no longer transports water. It is usually darker and often more naturally durable due to extractives.
Read the definitionThe glossary
The trade terms you'll come across.
Plain-English definitions for the words that turn up when you're buying, specifying or working with timber.
Heat treatment
Thermal modification of wood at 180-230°C in a low-oxygen environment to permanently alter its properties. Reduces moisture absorption, increases dimensional stability and decay resistance, and darkens the wood.
Read the definitionHelical thickenings
Spiral ridges on the inner surface of tracheid cell walls, visible under magnification. Diagnostic feature in species identification.
Read the definitionHemicellulose
A group of carbohydrates in plant cell walls that bind with cellulose and help form the matrix of the wood cell wall.
Read the definitionHoneycomb
An internal drying defect characterised by cracks inside the timber that are not visible on the surface. Caused by drying too rapidly before moisture can migrate from the core. Often undetected until the board is sawn or planed.
Read the definitionHoneycombing
Internal cracking that creates a honeycomb-like pattern of voids within the wood, caused by excessive drying stress before the moisture gradient has equalised.
Read the definitionHygrometer
A hygrometer is a device that measures relative humidity (and often temperature). In woodworking it’s used to understand the environment’s EMC range and anticipate moisture content changes and seasonal movement.
Read the definitionHygroscopic
Able to absorb and release water vapour from the air. Wood is hygroscopic, so it continuously exchanges moisture with its environment.
Read the definitionImpact resistance
The ability of wood to absorb sudden energy loads without fracturing. High impact resistance is critical for tool handles, sporting goods, and flooring.
Read the definitionInclusion
A foreign material or abnormal tissue trapped within the wood structure, such as bark, mineral deposits, or insect debris.
Read the definitionIntercellular canals
Tubular passages in wood that carry resin or gum, surrounded by specialised secretory cells. Characteristic of species like pine, spruce, and some tropical hardwoods.
Read the definitionInterlocked grain
Grain where the fibre direction alternates (often in bands) so that it reverses direction repeatedly through the wood.
Read the definitionInternal stress
Internal stress is stress locked into timber that can be released by sawing, planing, or drying. It can come from growth stresses formed in the living tree or from drying stresses created by moisture gradients.
Read the definitionJanka hardness
A standard test of wood hardness that measures the force required to press a steel ball into wood to half the ball’s diameter.
Read the definitionJointing
Creating a perfectly straight, flat reference edge on a board using a jointer or hand plane. The jointed edge serves as the baseline for subsequent ripping and surfacing operations.
Read the definitionJuvenile wood
Juvenile wood is the wood formed in the early years of a tree’s growth, typically found nearer the pith. It often has different properties from mature wood (e.g., higher longitudinal shrinkage, lower stiffness in some species, and greater tendency to distort), which can make boards cut near the centre more troublesome.
Read the definitionKerf
Kerf is the width of material removed by a saw cut—the thickness of the slot left behind. Kerf affects yield (waste), cutting power, and surface quality; thinner-kerf blades generally waste less wood.
Read the definitionKiln drying
The controlled process of removing moisture from timber using heat and airflow in a chamber. Kiln drying accelerates the natural seasoning process, reducing moisture content to a target level (typically 6-8% for furniture, 12-18% for construction) in days rather than months.
Read the definitionKnot
The cross-section of a branch embedded within the tree trunk. Knots interrupt the grain flow, reducing strength and complicating machining. Classified as live (attached) or dead (detached, prone to falling out).
Read the definitionLap joint
A joint where two overlapping pieces of wood are joined together. One of the simplest wood joints, suitable for framing and box construction.
Read the definitionLatewood
Wood formed later in the growing season when growth slows, typically darker and denser (with smaller cells and thicker walls).
Read the definitionLignin
A complex polymer in wood cell walls that acts like a natural adhesive, binding cells and giving wood rigidity and compression strength.
Read the definitionLongitudinal
The direction along the grain, parallel to the tree trunk axis. Most wood strength and stiffness is greatest in this direction.
Read the definitionLongitudinal shrinkage
Longitudinal shrinkage is the change in length of wood as moisture content changes below fibre saturation point. In normal mature wood it is usually very small (~0.1–0.3% from green to oven-dry), but it can be much higher in juvenile wood and reaction wood.
Read the definitionLumber
Timber that has been sawn and at least partially planed, ready for construction or woodworking. The North American term for sawn timber.
Read the definitionMarking gauge
A woodworking tool consisting of a beam with a marking pin or knife that scribes lines parallel to a reference edge at a set distance.
Read the definitionMDF
Medium density fibreboard — an engineered panel made from wood fibres bonded with resin under heat and pressure. Uniform density and smooth surface, widely used for painted cabinetry.
Read the definitionMedullary rays
Bands of cells that run radially from the centre of the tree toward the bark, used by the living tree for storage and transport across the trunk.
Read the definitionMicroclimate
A microclimate is a local zone where temperature and humidity differ from the surrounding space (e.g., near radiators, exterior walls, inside cabinets). In woodwork, microclimates can cause uneven moisture exchange and lead to cupping or distortion.
Read the definitionMicrofibril angle (MFA)
Microfibril angle (MFA) is the angle between cellulose microfibrils in the S2 layer of the cell wall and the cell’s long axis. Lower MFA generally increases stiffness and keeps longitudinal shrinkage low; higher MFA (common in juvenile and reaction wood) increases longitudinal shrinkage and distortion risk.
Read the definitionMineral streak
Dark discoloured bands running along the grain, formed by chemical deposits (often iron) accumulated in the tree. Common in walnut and oak.
Read the definitionMixed lengths
Lumber sold with a range of board lengths in a bundle rather than sorted to a single length. Common for lower-grade hardwood lumber.
Read the definitionModulus of elasticity
A measure of wood stiffness — the ratio of stress to strain under bending load. Indicates how much a board will deflect under load. Also called MOE.
Read the definitionMoisture content
The amount of water in wood expressed as a percentage of the oven-dry wood mass.
Read the definitionMoisture gradient
The difference in moisture content between the outer layer (shell) and inner core of a piece of timber during drying. A steep gradient causes drying stresses that lead to checking, honeycombing, and case hardening.
Read the definitionMoisture gradient
A moisture gradient is a difference in moisture content between the surface and the core (or between faces) of a piece of wood. Gradients create internal stress during drying and can cause distortion when material is removed or conditions change quickly.
Read the definitionMortise and tenon
A woodworking joint where a protruding tenon on one piece fits into a matching mortise (slot) on another. One of the strongest and oldest wood joints, used in framing and furniture.
Read the definitionMovement factor
The degree to which wood expands and contracts with changes in moisture content. Tangential shrinkage is typically 1.5-2x radial shrinkage, causing significant movement in flat-sawn boards.
Read the definitionMultiseriate rays
Wood rays more than one cell wide, visible as broader horizontal bands in cross-section. Characteristic of most hardwoods.
Read the definitionNailability
The ease of driving nails into wood and their holding power once set. Determined by density and fibre structure. Dense hardwoods resist nailing but provide strong holding power.
Read the definitionNo. 1 Common
Second-grade NHLA hardwood lumber with minimum clear-face yield of 66-2/3%. Suitable for furniture components and smaller parts.
Read the definitionNo. 2A Common
A lower grade in the NHLA grading system with minimum clear-face yield of 50%. Suitable for furniture and cabinetry parts that are 3 inches or smaller.
Read the definitionNominal vs actual dimension
The difference between the stated size of lumber (nominal) and its final dimension after drying and planing (actual). A 2x4 nominal board measures approximately 1.5" x 3.5" actual.
Read the definitionOpen grain
A wood texture where pores/vessels are large and prominent, leaving visible open pores on the surface (often requiring grain filling for a glass-smooth finish).
Read the definitionOSB
Oriented strand board — an engineered panel made from compressed wood strands oriented in specific directions. Replaces plywood in many structural applications.
Read the definitionParenchyma
A general term for living wood cells that store and transport nutrients (in rays and axial bands). In timber, parenchyma can appear as light streaks or bands.
Read the definitionParticleboard
An engineered wood panel made from wood chips, sawmill shavings, or sawdust bonded with synthetic resin and pressed. Cheaper than MDF but less dense.
Read the definitionPEFC certification
Programme for the Endorsement of Forest Certification — an umbrella organisation promoting sustainable forest management through independent third-party certification. The world's largest forest certification system.
Read the definitionPerforation plates
The specialised end walls between vessel elements in wood, with openings (perforations) that allow water flow between adjacent cells. Type varies by species.
Read the definitionPermeability
The degree to which fluids and gases can pass through wood. Affects drying rate, treatability with preservatives, and movement of moisture during service.
Read the definitionPhloem
Living tissue in a tree that transports sugars and other products of photosynthesis from leaves to the rest of the plant.
Read the definitionPiling
The organised stacking of lumber for seasoning or storage, ensuring proper sticker placement, weight distribution, and protection from ground moisture.
Read the definitionPin knots
Very small knots (less than 6mm diameter) typically from small branch growth. Common in species like cherry and maple. Considered attractive in furniture grade rather than a defect.
Read the definitionPith
The small central core of a tree stem around which the first growth formed. It is typically less stable and often associated with cracking and distortion when included in boards.
Read the definitionPitting
The arrangement of pits (thin areas in cell walls) that allow communication between adjacent cells. Inter-vessel pitting patterns are important for microscopy-based identification.
Read the definitionPlain-sawn (flat-sawn)
Plain-sawn (also called flat-sawn) describes boards cut tangentially to the growth rings so the rings meet the face at a low angle (often ~0–30°). It maximises yield and width, often shows “cathedral” grain, and is generally more prone to cupping than quarter-sawn stock.
Read the definitionPlaned all round
Lumber (usually British terminology) that has been planed on all four faces to a smooth finish. Equivalent to S4S in North America.
Read the definitionPlaning
The process of smoothing a wood surface with a plane or planer, creating a flat, dimensioned board. Essential for achieving precise joint fit and finish.
Read the definitionPlywood
An engineered wood panel made by gluing together thin sheets (veneer) of wood with alternating grain direction. The cross-lamination creates uniform strength in all directions.
Read the definitionPollarding
A woodland management practice similar to coppicing but performed higher up the trunk, above browse height. Allows regrowth while protecting new shoots from grazing animals.
Read the definitionPressure treatment
A process where chemical preservatives are forced deep into wood fibres under high pressure, significantly extending the service life of timber exposed to decay, insects, and moisture. Common for outdoor decking, fencing, and structural applications.
Read the definitionProng test (fork test)
The prong test (fork test) is a simple check for case hardening: rip a board down the middle and observe whether the two halves spring outward (case hardened) or stay straight (minimal stress).
Read the definitionQuarter-sawn
Boards cut so the growth rings are closer to perpendicular to the wide face (typically 60–90° ring angle), exposing more radial grain.
Read the definitionQuilted figure
A three-dimensional blistered appearance in wood, resembling a patchwork quilt surface. Most associated with Pacific bigleaf maple. One of the rarest and most prized decorative figures.
Read the definitionRabbet
A rectangular recess cut into the edge of a board, creating a step or L-shaped profile. Used in cabinet joinery and case construction.
Read the definitionRadial
Direction from the pith outward to the bark, crossing growth rings at right angles. One of the main axes used to describe wood movement and properties.
Read the definitionRaised grain
A condition where the hard latewood stands above the softer earlywood after planing, creating a textured surface caused by dull tools or high moisture content.
Read the definitionRay fleck
Ray fleck is the shimmering or ‘flake’ figure seen on the face of some quarter-sawn hardwoods (especially oak), caused by large medullary rays being cut and exposed. It’s a visual indicator of a radial surface and is often associated with improved stability.
Read the definitionRay parenchyma
Horizontal wood tissue extending radially from the pith toward the bark, responsible for lateral transport and storage of nutrients. Visible as flecks and rays in quarter-sawn timber.
Read the definitionRays
Radial sheets or ribbons of cells running from the centre of the tree outward. On end grain they appear as fine radial lines, and on quarter-sawn faces they can produce ray fleck figure.
Read the definitionReaction wood
Wood with abnormal structure formed by a leaning or stressed tree to correct its posture. It can have unusual shrinkage and internal stress behaviour.
Read the definitionReconditioning
A kiln process applied after drying to relieve internal stresses and case hardening by reintroducing some moisture through steaming or controlled humidity.
Read the definitionReforestation
The replanting of trees on land where forests have been cut down or destroyed, restoring forest cover and ecological function.
Read the definitionRegeneration
The process of renewing a forest stand through natural seeding, planting, or artificial means. Essential for sustainable forest management.
Read the definitionRelative humidity (RH)
Relative humidity (RH) is the percentage of water vapour in the air compared with the maximum the air could hold at the same temperature. RH strongly controls wood’s equilibrium moisture content (EMC), and therefore moisture content and movement.
Read the definitionResin canals
Specialised tubular channels in some softwoods (and a few hardwoods) that contain and transport resin (oleoresin).
Read the definitionResin duct
A specialised tubular structure in softwoods (conifers) that produces and stores resin. Normal resin ducts are anatomically consistent; traumatic resin ducts form in response to injury.
Read the definitionReticulate parenchyma
Parenchyma cells arranged in a net-like or reticulated pattern, forming an interconnected system within the wood structure.
Read the definitionRibbon stripe
Alternating bands of light and dark caused by cutting interlocked grain on a quarter, revealing the alternating grain direction as parallel stripes.
Read the definitionRift-sawn
Boards cut so the growth rings meet the face at roughly 30–60° (often aiming near 45°), producing very straight, uniform grain.
Read the definitionRing shake
Complete separation of adjacent growth rings, creating a gap in the wood. Weakens the board and creates potential failure points.
Read the definitionRing-porous
A hardwood where the pores (vessels) are much larger in earlywood and smaller in latewood, forming a distinct pore band each growth ring.
Read the definitionRipping
Cutting wood along the grain (parallel to the fibres), typically separating fibres and following the board’s length direction.
Read the definitionRot
Advanced wood decay caused by wood-destroying fungi, classified as brown rot, white rot, or soft rot. Each type attacks different wood components (cellulose, lignin, or both).
Read the definitionRough milling
Rough milling is the process of machining wood slightly oversize (in thickness/width) and then letting it rest so stresses can redistribute and moisture can equalise before final milling to finished dimensions.
Read the definitionRough sawn
Lumber that has been sawn to size but not been surfaced or planed, retaining the rough texture from the saw.
Read the definitionRouting
Machining decorative profiles, grooves, or shaped edges using a router with a cutting bit. Common for mouldings, dados, and custom edges.
Read the definitionRunout
Grain deviation where wood fibres are not parallel to the length of the board, causing fibres to ‘run out’ of the face or edge.
Read the definitionS2 layer
The S2 layer is the thickest layer of the secondary wall in most wood cells. It contains most of the cell wall’s cellulose microfibrils and largely controls stiffness and shrinkage behaviour, including the effect of microfibril angle on longitudinal movement.
Read the definitionS2S
Surfaced Two Sides — lumber that has been planed on the two broad faces but left rough on the edges.
Read the definitionS4S
Surfaced Four Sides — lumber that has been planed flat on all four faces, dimensioned to consistent thickness and width.
Read the definitionSanding
Surface finishing using abrasive paper to smooth wood, removing tool marks and preparing the surface for finish application.
Read the definitionSapwood
The outer, younger wood in a tree that actively transports water and nutrients when the tree is alive.
Read the definitionScariform perforation
A specific type of vessel end wall perforation pattern in wood, with horizontal bars resembling ladder rungs. Important for microscopic species identification.
Read the definitionSeasoning
The process of drying green (fresh-cut) timber to reduce its moisture content to a level appropriate for its intended use. Proper seasoning prevents warping, cracking, and structural failure.
Read the definitionSelective felling
A harvesting method where only selected mature trees are cut, leaving the rest of the stand to regenerate naturally. More ecologically sustainable than clear felling.
Read the definitionSelects
NHLA grade for softwood lumber, appearance-graded for finish quality. The best face is nearly free of defects, suitable for painting or staining.
Read the definitionShake
A separation between growth rings, usually caused by failure along the ring boundary (often from growth stress, frost, or mechanical damage).
Read the definitionShear strength
The ability of wood to resist forces that cause sliding failure along the grain. Important for joints, fasteners, and load-bearing connections.
Read the definitionShooting board
A precision jig used with a hand plane to accurately trim board edges to exact angles (90° or custom bevels) in repeatable fashion.
Read the definitionStuck on something?
Ask Shane
I don’t sell timber, but I’ll help you work out what you actually need and where to find it.