jamb: The vertical side members of door or window frame, including the frame itself.

Janka: A unit of measure used to describe the surface hardness of wood. A Janka rating is determined by the amount of force required to drive a 0.444 inch steel ball half its diameter into the wood product.

joint: The edge where two touching members or components come together.

joint staggering: The process of laying flooring planks such that the places where the ends meet do not fall next to each other, but rather are staggered across the width of the floor.

jointed flooring: Strip flooring, usually birch, beech , hard maple or pecan manufactured with square edges and no tongue or groove usually end matched. Used principally for factory floors where square edges make replacement of strips easier.

joist: One of a series of parallel beams used to support floor or ceiling loads and supported by larger beams, girders, or bearing walls.

juvenile wood: Wood formed early in the life of a tree, and is therefore at the center of the tree.