(1) A knot which is a portion of a branch and which has become incorporated in the body of a tree. All provisions of this chapter relating to the presence of knots apply only to the surface of the piece on which the knot appears, and all such provisions limiting the size of knots apply to the mean or average diameter as measured on the surface.

(2) Cross-grained wood in which the fibres are not parallel with the axis or longitudinal edge of the piece. It is expressed in this chapter as the slope of the grain with respect to the edges of the piece. For instance, one in 12 means that in a distance of 12 inches the grain deviates one inch from the edge. The presence in any surface of local discontinuity of grain or local deviations in the straightness of grain because of knots permitted in the piece shall be disregarded in applying the provisions of this chapter.

(3) A shake which is a separation along the grain, the greater part of which occurs between the rings of annual growth.

(4) A check which is a separation along the grain, the greater part of which occurs across the rings of annual growth.

(5) A pitch pocket which is an opening between the grain of the wood, containing more or less pitch or bark.

(6) Decay which is the destruction of the wood substance due to the action of wood destroying fungi.

(7) A cross-break which is a separation of the wood cells across the grain of the wood.

(8) A compression failure which is a deformation of the fibres due to excessive compression along the grain. This deformation takes the form of a buckling of the fibres.

(9) Compression wood, or proudwood, which is an abnormal growth occurring in conifers (softwood) and is characterized by relatively wide annual rings, usually eccentric and a comparatively large proportion of summerwood, usually 50% or more, which merges into the springwood without exhibiting a marked contrast in color.