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Lumber is divided into 3 main categories - hardwoods, softwoods and engineered.
Hardwoods (Oak, Cherry, Mahogany) are sold by the board foot.
Softwoods (Pine, Firs, Larches) are mostly sold as 'dimensional' lumber, sawn and surfaced to a particular size (like 2X4in studs) for construction.
Engineered lumber would include plywood, laminated beams, and butcher blocks.