Softwood
Wood from conifers, such as pine, spruce, and fir. Generally used for framing.

Hardwood
Wood from deciduous trees, such as oak, birch, and maple. Used for finish work, such as flooring, cabinetry, and moldings. The term can deceive: The relative hardness of some softwoods is more than some hardwoods.

Nominal Dimension
The nicknames for lumber sizes. Softwood dimensions give thickness and width, as in 2x4 ("two-by-four") or 1x8. Hardwood dimensions give only thickness, expressed as a fraction over 4, as in 4/4 ("four-quarter") for 1 inch, or 12/4 for 3 inches. Nominal dimension is an artifact that no longer equals actual dimension.

Actual Dimension
Lumber's exact size, always smaller than nominal. A 2x4 is about 11?2 inches by 31?2 inches.

Dimensional Lumber
(aka dimension lumber) Wood cut into standard sizes, such as 2x4, 1x6, etc. "Dimension" and "dimensional" are often interchangeable. However, some limit use of the term "dimension lumber" to wood between 2 and 5 inches thick (nominally) and use "dimensional lumber" to distinguish solid wood from engineered lumber.

Board
Lumber thinner than 2 inches (nominal dimension).

Timber
Lumber thicker than 5 inches (nominal dimension).

Engineered Wood
Lumber and panels made from wood fibers or veneers glued or molded together, as with plywood, medium density fiberboard (MDF), or laminated veneer lumber (LVL).

Pressure Treated Lumber
Wood treated under pressure with minerals to make it resistant to rot and insects.

Board Foot
A measure used to price exotic and other woods not milled to standard sizes; equal to 144 cubic inches.

Seasoned
Dried to reduce wood's natural moisture and make it lighter and less likely to deform.

Kiln Dried
Seasoned by baking with dry heat in a special room.

Air Dried
Seasoned naturally by stacking.

Heat Treated
Heated with steam or in a kiln to kill insects and make wood more stable against swelling and shrinking.

Green
Freshly sawn or not yet seasoned and dried.

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