Burl – A defect in wood resulting from the tree undergoing stress, such as the growth of a mold or fungus. This produces an unusual grain pattern that is prized and sought after in wood flooring and furniture.

Butt end – The place where two wood planks of the same row come together. The standard industry practice is to have tight butt joints that are barely visible from a standing position. Certain problems can cause butt ends to gap and become apparent in a wood floor, such as incorrect installation or planks with unsquare ends.

Case hardening – A defect that occurs when lumber has dried too rapidly. The outer layer (shell) of the wood begins to shrink while the core retains its moisture content. The core resists this shrinkage, resulting in tension with the shell. Case hardening often results in surface checking, and excessive warping can occur when the tension is released via sawing.

Character – Character markings in a wood floor includes defects such as knots, wormholes, and nail holes. These features are often present in Select, No. 1 Common, and No. 2 Common grades of wood. They are also featured in distressed and reclaimed hardwood floors.

Checking – A check is an opening on the surface of the wood, often resulting from case hardening.

Crowning – Crowning occurs when the center of a board swells and becomes higher than the edges. This is often caused by excess moisture in the wood. Crowning can also be brought about when a cupped floor is sanded down while the moisture content in the floor is still elevated.

Cupping – Cupping occurs when a hardwood floor swells due to excess moisture. The edges of the boards push together, raising them above the center of the boards and creating valleys or “cups”. Both cupping and crowning can be prevented by proper moisture measurements taken before, during, and after the wood floor installation process.

Cut Nails – A type of flooring nail that is frequently used to replicate the look of old-fashioned carpentry. Unlike a modern flooring nail, the head of a cut nail appears at the surface of the wood. Cut nails must be installed manually and are frequently found in reclaimed and hand-distressed hardwood flooring.

Defecting – Flaws in wood resulting from stress, mistakes during the milling process, etc. In hand-distressed flooring, defects like nail holes, scratches, and dents are purposefully created to impart the wood with a vintage look.

Dimensional Stability – The measurement of how much or how little a wood plank shrinks or expands in response to the relative humidity of the air surrounding it. More dimensional stability means that the wood will respond less to the moisture in its environment. Each wood species possesses a unique level of dimensional stability.

Engineered – Engineered wood floors feature either a composite fiberboard or plywood base underneath a thin top veneer (usually ranging from 0.6 mm to 4 mm thick) of solid wood. Engineered flooring is more dimensionally stable than solid wood and is therefore suitable for installation in below-grade environments and over radiant heat systems.

Filled – A wood floor is considered “filled” when a mixture of material is placed into open knots or voids, making the floor’s appearance more uniform.

Flecking – Flecking is a wood characteristic that is present in quarter-sawn planks with medullary rays. Flecks are the exposure of these rays, which results in unique figure variants in the wood.

Grade – The grading of wood is based on the percentage of defect-free boards in a selection. The typical grades of unfinished oak hardwood floors are: Clear, Select, No. 1 Common, and No. 2 Common.

Clear: The “cleanest” possible grade of a hardwood floor. Little variation in color and exceptional average board length, no knots or other defects in the wood.

Select: Usually contains a small amount of color. Minimal character markings, and average overall length. The most widely used grade.

No. 1 Common: Color variation and character markings such as small knots and mineral streaks. Moderate color variation between sapwood and heartwood. Less average length per board.

No. 2 Common: Significant manufacturing marks and character marks. Prominent color variation between sapwood and heartwood. Short overall length.

Hand-planed – Also known as “hand-scraping”, hand-planing is the act of sculpting the surface of wood planks to give the floor a textured, worn look. Hand-planing is frequently used to create hand-distressed wood flooring.

Hand-scrapped – Also known as “hand-planing”. See above definition.

Heartwood – The inner portion of a tree. Heartwood is usually darker in appearance than the outer, living layer (sapwood). Heartwood is also more durable and rot-resistant than sapwood.

Honeycomb – Internal checks in a piece of lumber. Honeycombs develop in wood that has been improperly dried in the kiln, so they are often present in case-hardened wood. Honeycombs diminish the stability and strength of a floor plank.

Janka Hardness Rating – A measurement of the durability of a wood species. The Janka hardness test is performed by measuring the force required to embed a .444-inch steel ball into a plank of wood until half of the ball’s diameter is embedded. The resulting measurement is recorded in pounds-force (lbf). Janka hardness is useful for comparing the durability of one species to another.

Kerf Cuts –These marks, also referred to as “kerf marks”, are created by a saw cutting through wood. Kerf cuts are sometimes intentionally created in hand-distressed wood flooring to produce a reclaimed, rustic look that often resembles a hand sawn beam.

Knots – A knot is a defect in wood that usually appears as a dark, circular spot on the surface, around which the grain of the wood flows. Knots are prevalent in No. 1 Common and No. 2 Common grades of wood. Although they are technically a defect, knots are often prized for their aesthetic appeal.

Live Sawn – A method of cutting wood in which the log is sawn all the way through the diameter, allowing the heart of the log to be utilized. Other methods of sawing, including plain sawing, leave out the heart of the log. Live sawing allows the character and variation that is present throughout the entire log to make an appearance in all or most of the flooring planks.  A unique trait of the live sawn cut is the mixture of Rift, Qtr’d and Plain Sawn material in the same floor boards.

Longitudinal Shrinkage – The lengthwise shrinkage of wood during the process of drying from “green” to “oven-dry”. Longitudinal shrinkage normally ranges from about 1/20″ to 1/10″ in a board that is 8 feet long. Excess longitudinal shrinkage can occur under certain conditions and in certain types of wood, including springwood and compression wood.

Milled Face – Milled face means that each piece of reclaimed lumber is “milled” or planed. Take a barn beam, for example. It has four “original faces”, which are then machined to remove “the original face”.  Milled face floors are more consistent in color than natural face floors because the imperfection and color inconsistency is planed out of the board face revealing clean material from under the original face.

Moisture Content – The amount of moisture present in the wood or subfloor at a given point in time. The moisture content of a piece of wood is dependent on the relative humidity of the air surrounding it and how it was dried at the mill – the higher the relative humidity, the higher the moisture content of the wood. The moisture content of a wood floor and the subfloor must be at the correct levels before, during, and after installation to prevent problems like cupping and crowning. Each region of the country has an average Equilibrium Moisture Content (EMC) based on the relative humidity of the region.

Original Face – The surface of flooring which remains untouched during the milling process. When original face wood is milled, the lumber is not sanded down. As a result, the floors retain the original patina, character markings, and defects of the source.

Original Face Reclaimed Plank – With original face reclaimed plank flooring, the patina of the original wood – along with any saw marks, nail holes, and other character marks – remain in the floors, giving them a rustic look.

Patina – The change in wood’s color over time resulting from exposure to UV rays and other natural elements. As a hardwood floor ages and oxidation occurs, a patina is created on the surface of the wood, changing its appearance.

Photosensitive Resins – Substances in wood that react to exposure to UV rays by changing color. Certain wood species, such as American cherry, contain more photosensitive resins than others, resulting in drastic changes in the wood’s appearance with the passage of time.

Pillowed Edge – A type of soft round bevel at the edge of an engineered flooring board.

Plain Sawn – Also referred to as flat sawn, this is a method of sawing lumber in which the log is cut tangential to the growth rings, creating a “cathedral window” pattern on the face of the board. The plain sawn method is the most common and least expensive form of milling wood, but it is less dimensionally stable than rift and quartered wood.

Plywood – A common type of subfloor comprised of multiple cross-directional layers of wood — usually a species of southern yellow pine — that are glued together for dimensional stability.

Pre-sanded – Refers to a hardwood floor that is sanded by hand or at the mill rather than on-site. Engineered hardwood floors are typically pre-sanded and prefinished.

Reclaimed Wood – Wood that has been repurposed from its original application. Reclaimed wood floors are typically sourced from barns, older homes, and industrial and commercial buildings. The process of reclaiming floors reduces waste and the demand for newly milled wood.  Reclaimed wood floors are sought after because they typically contain nail holes, character markings, and the original patina, all of which lend a rustic look to the space in which they are installed.

Reclaimed Barnwood Paneling – Interior wall and ceiling paneling that is milled from antique barnwood. The patina and character markings of the original wood remain, creating a worn-in, rustic style.

Reclaimed Milled Barnwood – Barnwood that is milled into reclaimed hardwood floors. As with barnwood paneling, milled barnwood floors showcase the original patina, character markings, and defects in the wood to produce an antique look.

Relative Humidity – A measurement of the amount of water vapor present in the air at a given time. It is important to monitor the relative humidity levels in a space before, during, and after the installation of hardwood floors. Wood is hygroscopic, meaning that it absorbs and releases moisture from the surrounding environment. Relative humidity levels that are too high or too low can contribute to moisture problems in wood floors, such as cupping and gapping.

Rift & Quartered – A combination of rift sawn and quarter sawn milling, rift and quartered wood floors exhibit vertical and radial graining. Rift and quartered floors have extra strength and durability compared to wood floors that have been milled using other methods.

Sapwood – One of the outer layers of a tree that lies between the bark and the heartwood. Sapwood is the younger growth of the tree. In flooring, sapwood planks are typically lighter in color with domestic species than planks consisting of heartwood.

Scraping – A technique used to enhance the character of the wood by sculpting each individual plank to create subtle grooves and indentations. The hand-scraping technique is frequently used in the creation of hand-distressed wood flooring.

Select – Select grade wood is second-best to clear grade with regard to clarity and lack of blemishes in the wood. Select wood floors typically exhibit uniform color throughout the planks, a minimal amount of character markings, and greater length than one common material.

Sliced vs. Rotary Peeled – These are two different ways of creating solid wood veneers for engineered wood flooring. Rotary peeled veneers are created by cutting in a circular motion from the outside of a wood log into the center, whereas sliced veneers (also known as plane sliced veneers) are created by cutting lengthwise from one end of a log through to the other end. Rotary peeled veneers create a wide grain effect, and the rotary peeling process creates less waste than the process of slicing a veneer. However, sliced veneers are more stable and match the original grain pattern of the wood more closely than rotary peeled veneers.

Solid – As opposed to engineered wood (which consists of a veneer of wood on top of a plywood or composite base), a solid wood floor is composed of the same species of wood all the way through. Solid wood is more natural looking than engineered wood. However, solid wood is less dimensionally stable and therefore unsuitable for installation in below-grade environments.

Southern Yellow Pine (SYP) – A group of pine species which includes slash, longleaf, loblolly, and shortleaf pines. Southern yellow pine floors are renowned for their prominent knots and distinctive graining patterns.

Steamed – Steamed wood – when referring to the American Walnut species – is a process that minimizes the starkness between the darker heartwood and the lighter outer layer of sapwood.

Tannins – Tannins are naturally occurring compounds found in wood. Certain wood species contain more tannins than others. The tannins in various wood species react differently to stains and finishes, and therefore must be accounted for in the hardwood floor installation process.

Tight Knots – Unlike other types of wood knots, tight knots do not negatively affect the strength and integrity of the wood.

Tongue and Groove – The tongue is milled on one edge of a plank, while the groove is cut on the opposite edge. The tongue of a board fits into the groove of another board to connect the planks for installation.

Tyloses – Membranous outgrowths of xylem vessels present in the heartwood of a tree. Different wood species have different degrees of open or closed tyloses. Closed tyloses make a wood species more water-resistant than a species with open tyloses.

Worm holes – A tiny round hole in hardwood flooring made by a small wood-boring insect. Worm holes are often found in reclaimed wood. The source of the holes is eliminated during the kiln drying process.

Shake – This refers to the lifting of the portion of wood flooring near or around the growth ring. “Wind shake” is typically caused by environmental conditions, such as high winds.

Through knots – Knots that run from one side of the board to the other.