Xylem - part of a tree between the bark and the pith which forms the mechanical structure that constitutes the wood from which the fibre is obtained for use in pulp and papermaking.

Yield - ratio of total amount of raw material entering a pulp and papermaking operation to the equivalent product output.

Z-Directional Strength - the strength of paper and board as related to the force and measured by means of tension applied to the surfaces of the test sample.