# Wood flooring glossary

> Plain-English definitions of 54 wood flooring terms, each tied to a cited source such as the USDA Wood Handbook, NWFA technical publications, FEP, European standards listings and The Wood Database. Where a term has more than one usage, the glossary says so.

Source page: https://www.misterendgrain.com/glossary/
Updated: 2026-11-03

This glossary explains the terms you meet when you read about wood floors. Definitions come from the sources listed at the foot of the page: mainly the USDA Forest Products Laboratory, technical publications of the US National Wood Flooring Association (NWFA), the European Parquet Federation (FEP), standards listings and The Wood Database. A few terms, such as chevron and underlay, have no standards-body definition, so they rely on named manufacturers' descriptions and say so. For deeper reading, follow the links to our [guides](https://www.misterendgrain.com/guides/janka-hardness-explained/) and [flooring types](https://www.misterendgrain.com/flooring/engineered-wood/).

## A

**Acclimatisation**: The process of allowing a wood floor's moisture content to equilibrate with the environment in which it will perform [2]. The NWFA now suggests "conditioning" is the more accurate word, because the aim is to prepare the building for the flooring rather than to alter the wood [7]. See our [guide to moisture and acclimatisation](https://www.misterendgrain.com/guides/moisture-and-acclimatisation/).

**Air-dried**: Wood dried by exposure to air in a yard or shed, without artificial heat [1].

## B

**Brinell hardness**: A measure of resistance to indentation used for wood flooring. The 2000 edition of the European test standard EN 1534 was titled "Wood and parquet flooring – Determination of resistance to indentation (Brinell)"; the current 2020 edition is titled "Wood flooring and parquet – Determination of resistance to indentation – Test method" [11]. Compare [Janka hardness](https://www.misterendgrain.com/guides/janka-hardness-explained/).

## C

**Checking**: A lengthwise separation of the wood that usually extends across the growth rings and commonly results from stresses set up during seasoning [1].

**Chevron**: A parquet pattern whose boards form a "V" formation, as Kährs describes it [19]. BOEN describes its chevron as laid at a precise 60-degree angle [16]. See [chevron flooring](https://www.misterendgrain.com/flooring/chevron/).

**Click joint**: A glueless joint system. Kährs says it introduced the first parquet floor with its glueless Woodloc® joint in 1999 [21], and BOEN lists a "5G Click connection" on its planks [17].

**Compression set**: A permanent narrowing or crushing of the board edges that occurs when boards swell after a substantial moisture increase while adjacent boards stop them expanding [2].

**Cupping**: A concave or dished appearance of a board, with the edges raised above the centre, caused by a moisture imbalance through the thickness of the board, where the bottom is wetter than the top [2]. See also *warp* and *crowning*.

**Crowning**: The opposite of cupping: a convex appearance with the centre of the board higher than the edges, caused when the top of the board is wetter than the bottom [2].

## D

**Dimensional stability**: The degree to which a piece of wood maintains its manufactured dimensions when temperature and humidity change [2].

## E

**Earlywood and latewood**: The two parts of a growth ring. Earlywood forms early in the growing season and is usually less dense and weaker; latewood forms after it and is usually denser and stronger [1].

**End grain**: Wood cut so the growth rings face up, a transverse cut [2]. The NWFA notes that end-grain blocks are sometimes classified among parquet patterns [3]. See [end grain flooring](https://www.misterendgrain.com/flooring/end-grain/).

**End-lift**: Board ends that appear raised. The NWFA says this is very common with engineered flooring that has experienced an increase in moisture [2].

**Engineered wood flooring**: In the NWFA definition, real wood from top to bottom, normally made from multiple veneers or slats of wood glued together at opposing directions. "Composite engineered" flooring has real wood on the wearable surface only, with a backing or core of any composite material [6]. See [engineered wood flooring](https://www.misterendgrain.com/flooring/engineered-wood/).

**Equilibrium moisture content (EMC)**: The moisture content at which wood neither gains nor loses moisture when surrounded by air at a given temperature and relative humidity [2] [1].

**Expansion gap**: Space left around the perimeter and at fixed obstructions so the floor can move. The NWFA installation guidelines give a minimum of ½ in. (12.7 mm) for parquet and a general rule of ¾ in. for solid strip and plank, and refer engineered floors to the manufacturer's recommendation [4]. Always follow the maker's instructions.

## F

**Fibre saturation point**: The stage at which cell walls are saturated and cell cavities are free of water, usually taken as about 30% moisture content, based on oven-dry weight [1].

**Figure**: The pattern produced in a wood surface by growth rings, rays, knots, deviations from regular grain such as interlocked and wavy grain, and irregular colouring [1].

**Flat-sawn**: See *plain-sawn*.

**Fuming**: Using ammonia vapour to darken wood. The fumes react with the natural tannins in certain species, and woods high in tannin, such as white oak, beech and butternut, respond best [13].

## G

**Gaps (seasonal)**: Separations between solid wood boards that open in winter when heated air lowers relative humidity. The NWFA calls them a normal phenomenon, says most close when humidity returns, and advises against filling them [2].

**Grade**: A designation of the quality of a manufactured piece of wood or of logs [1]. Makers use their own scales: BOEN, for example, groups its gradings as Calm, Lively and Rustic [15].

**Grain**: The direction, size, arrangement, appearance or quality of the fibres in wood. The term has a specific meaning only when qualified, as in straight grain or cross grain [1].

**Growth ring**: The layer of wood added to a tree during a single growing season [1].

## H

**Hardwax oil**: A floor finish based on plant oils and natural waxes. BOEN describes its Live Natural oil as containing sunflower, thistle or soya bean oil with carnauba and candelilla waxes [14]. Kährs notes that an oiled finish enhances the texture and grain of the wood [19]. See our [guide to wood floor finishes](https://www.misterendgrain.com/guides/wood-floor-finishes/).

**Hardwood**: Wood from broad-leaved trees, botanically angiosperms. The term does not necessarily refer to the actual hardness of the wood [2].

**Heartwood**: The wood extending from the pith to the sapwood, whose cells no longer take part in the tree's life processes. It is usually darker than sapwood [2].

**Herringbone**: Rectangular boards laid in a zig-zag so that they meet in a "point" [20]. The NWFA lists herringbone among geometric parquet patterns and notes that subfloor flatness is especially critical for it, typically within ⅛ in. over 10 feet [3]. See [herringbone flooring](https://www.misterendgrain.com/flooring/herringbone/).

**Hygroscopic**: Able to absorb and retain moisture, or give it up. Wood and wood products expand as they absorb moisture and become smaller as they lose it [2].

## J

**Janka hardness**: A measure of how well a wood resists denting. The figure is the force in pounds-force (lbf) or newtons (N) needed to embed a 0.444 in. (11.28 mm) steel ball into the wood to half the ball's diameter, normally on wood dried to 12% moisture content [8]. See [Janka hardness explained](https://www.misterendgrain.com/guides/janka-hardness-explained/) and the [hardness chart](https://www.misterendgrain.com/hardness-chart/).

## K

**Kiln-dried**: Wood dried in a kiln, a chamber with controlled airflow, temperature and relative humidity, using artificial heat [1].

**Knot**: The portion of a branch or limb that has been surrounded by subsequent growth of the stem [1].

## L

**Laminate flooring**: In the USDA glossary, a paper-based laminate is a multilayered panel made by compressing sheets of resin-impregnated paper into a solid mass [1]. This differs from engineered wood flooring, which the NWFA defines as real wood from top to bottom [6].

**Live-sawn**: A method of sawing straight through the log's diameter, leaving in the heart of the log and the grain variations found in all grades of lumber [2].

## M

**Medullary rays**: Strips of cells running from the bark toward the centre of the tree. Because they run perpendicular to the grain, they can add visual interest to finished flooring depending on how boards are cut [2].

**Moisture content**: The weight of the water in the wood expressed as a percentage of the weight of the wood itself [2]. The USDA expresses it as a percentage of the oven-dry weight [1].

**Moisture meter**: A tool for rapid determination of moisture content in wood by electrical means, in two main types: pinless (dielectric) and pin-type (electrical resistance) [2].

## P

**Parquet**: A term with a trade definition and a pattern meaning. For FEP, a product can be called parquet only if its real wood top layer is at least 2.5 mm thick, as set by European standard EN 13756 [9]; EN 13756 is itself the terminology standard for wood flooring and parquet [12]. The NWFA describes parquet as typically made of individual pickets assembled into panels held together by wire, mesh, tape or paperface [3].

**Plain-sawn (flat-sawn)**: Flooring cut so that the growth rings are mostly parallel, at 0° to 45°, to the wide face of the board, a tangential cut [2]. The USDA gives the same under 45° threshold for flat grain [1].

**Plank and strip**: The NWFA treats solid strip flooring as less than 3 in. wide and solid plank flooring as 3 in. wide or more when setting moisture tolerances [2]. See [wide plank flooring](https://www.misterendgrain.com/flooring/wide-plank/).

## Q

**Quarter-sawn**: Flooring cut so that the growth rings are mostly perpendicular, at 45° to 90°, to the wide face of the board, a radial cut [2]. The USDA lists quartersawn as another term for edge-grained lumber [1].

## R

**Refinishing**: Sanding and recoating a floor to renew it. FEP's refinishable programme identifies parquet whose wear or top layers are thick enough to be refinished, based on a minimum 2.5 mm real wood top layer [10]. See [sanding and refinishing](https://www.misterendgrain.com/guides/sanding-and-refinishing/).

**Relative humidity**: The ratio of the water vapour in the air to the amount the air would hold at saturation at the same temperature, usually expressed as a percentage [2].

**Rift-sawn**: Flooring cut neither parallel nor perpendicular to the growth rings, so that the rings make angles of 30° to 60° to the board face; also called bastard sawn [2].

## S

**Sapwood**: The active wood near the outside of the tree, usually lighter in colour than heartwood [2]. The USDA adds that it is more susceptible to decay under most conditions [1].

**Shrinkage and swelling**: A change in dimension due to a loss of moisture below the fibre saturation point (shrinkage), or a gain in moisture below it (swelling) [2].

**Solid wood flooring**: Flooring made from a single piece of wood sawn into boards or strips. Kährs notes that it expands and contracts with seasonal humidity, which makes it less format-stable than engineered flooring [19]. See [solid wood flooring](https://www.misterendgrain.com/flooring/solid-wood/).

**Subfloor**: The base the flooring is fixed or bonded to. The NWFA says wood subfloors must be flat, clean, dry, structurally sound, free of squeaks and free of protruding fasteners [5]. For solid strip flooring under 3 in. wide, it advises no more than 4% moisture content difference between acclimated flooring and subfloor [5].

## T

**Tongue and groove**: A kind of machined edge joint in which boards interlock along their edges [1].

## U

**Underlay**: A layer laid between subfloor and floor. BOEN's guide ties underlay to a floor that feels quiet, stable and comfortable, and lists moisture barrier, impact sound and footfall sound among its functions [18]. See [installation methods](https://www.misterendgrain.com/guides/installation-methods/).

## V

**Veneer**: A thin layer or sheet of wood. The USDA distinguishes rotary-cut veneer, cut on a lathe, from sawn veneer, produced by sawing [1].

**Versailles panel**: A pre-assembled square parquet panel. Havwoods describes the pattern as squares held together by what appears to be an interwoven mesh of wood strips, and says it takes its name from the Palace de Versailles [22]. See [Versailles panels](https://www.misterendgrain.com/flooring/versailles-panels/).

## W

**Warp**: Any variation from a true or plane surface. The USDA says warp includes bow, crook, cup and twist, or any combination of them [1].

**Wear layer**: The real wood layer at the top of an engineered or parquet board. In the NWFA definition of a wood floor, real wood is the top-most, wearable surface [6]; see also *parquet* for the 2.5 mm minimum [9].

## Sources

1. [Wood handbook: Wood as an engineering material (FPL-GTR-282), Glossary](https://research.fs.usda.gov/treesearch/62200), USDA Forest Service, Forest Products Laboratory, accessed 2026-11-03
2. [Moisture and Wood, Technical Publication No. A100 (2nd edition, 2017)](https://cdn.shopify.com/s/files/1/2953/2504/files/Moisture_and_Wood.pdf), National Wood Flooring Association, accessed 2026-11-03
3. [Ornamental Floors: Design and Installation, Technical Publication No. B300 (3rd edition, 2015)](https://cdn.shopify.com/s/files/1/2953/2504/files/Ornamental_Floors.pdf), National Wood Flooring Association, accessed 2026-11-03
4. [NWFA Guide 4: Installation Guidelines (revised 02.2016)](https://cdn.shopify.com/s/files/1/2953/2504/files/NWFA_Guide_4_-_Installation_Guidelines.pdf), National Wood Flooring Association, accessed 2026-11-03
5. [NWFA Guide 3: Subfloor Guidelines (revised 02.2016)](https://cdn.shopify.com/s/files/1/2953/2504/files/NWFA_GUIDE_3_-_Subfloor_Guidelines.pdf), National Wood Flooring Association, accessed 2026-11-03
6. [Real wood definition](https://nwfa.org/use-real-wood/), National Wood Flooring Association, accessed 2026-11-03
7. [Rethink Acclimation](https://hardwoodfloorsmag.com/2023/09/29/rethink-acclimation/), Hardwood Floors magazine (NWFA), accessed 2026-11-03
8. [Janka Hardness](https://www.wood-database.com/wood-articles/janka-hardness/), The Wood Database, accessed 2026-11-03
9. [Professionals](https://www.parquet.net/p/professionals.html), FEP, the European Parquet Federation, accessed 2026-11-03
10. [Parquet Refinishable Program](https://www.parquet.net/p/refinishable-program.html), FEP, the European Parquet Federation, accessed 2026-11-03
11. [NF EN 1534: Wood flooring, determination of resistance to indentation, test method](https://www.boutique.afnor.org/en-gb/standard/nf-en-1534/wood-flooring-determination-of-resistance-to-indentation-test-method/fa164917/36916), AFNOR, accessed 2026-11-03
12. [NF EN 13756: Wood flooring and parquet, terminology](https://www.boutique.afnor.org/en-gb/standard/nf-en-13756/wood-flooring-and-parquet-terminology/fa187129/81964), AFNOR, accessed 2026-11-03
13. [Fuming Wood with Ammonia](https://www.finewoodworking.com/project-guides/finishing/fuming-wood-with-ammonia), Fine Woodworking, accessed 2026-11-03
14. [Surface treatments](https://www.boen.com/en/guides/surface-treatments), BOEN, accessed 2026-11-03
15. [Grading systems](https://www.boen.com/en/guides/grading-systems), BOEN, accessed 2026-11-03
16. [Exquisite](https://www.boen.com/en/parquet/exquisite), BOEN, accessed 2026-11-03
17. [Plank 138 Oak White (product page)](https://boen.com/en/parquet/10036698), BOEN, accessed 2026-11-03
18. [Floor underlay](https://www.boen.com/en/guides/floor-underlay), BOEN, accessed 2026-11-03
19. [Wood flooring](https://www.kahrs.com/global/floors/wood-flooring), Kährs, accessed 2026-11-03
20. [Herringbone flooring](https://www.kahrs.com/global/floors/herringbone-flooring), Kährs, accessed 2026-11-03
21. [Our history](https://www.kahrs.com/global/b2b/about-us/our-history), Kährs, accessed 2026-11-03
22. [Versailles and other panels](https://www.havwoods.com/uk/selection/versailles-and-other-panels/), Havwoods, accessed 2026-11-03