undercoat: The first coat of finishing agent applied to a surface after preparation.

undercut: Cuts made that curve back under a projecting portion of a piece.

underrun: The situation where a mill expects to achieve a certain footage from a run and obtains less than expected.

Underwriters Laboratory: An independent, not for profit product safety testing and certification organization.

unfinished: A wood product that still has to be sanded and have finish applied.

uniform color: Lumber that is kiln dried, graded, surfaced, and then sorted for color so that the boards in one shipment are all in the same color tone family.

unsound knot: A knot that has cracks or voids or is noticeably softer than surrounding wood.

unsurfaced: Rough sawn.

urban wood: Used pallets, clean construction wood, repurposed lumber, flooring etc.

urethane: An elastic, petroleum based varnish commonly used to prefinish products at the factory.

UV Curing: A method of curing specially formulated top coats as ultra violet light causes quick and complete cross linking of the material.