The term "wane" is often used to describe missing areas on lumber. The term typically refers to defects on the ends or sides of the lumber, but wane can occur just about anywhere on milled wood. Wane is often associated with bark that remains on the lumber after it's milled.
Cause and Solution
Wane or skip is caused when surfacing machines or planers fail to remove all of the material from a low spot on the lumber. Wane can be removed by running the lumber through a planer, or it can be cut from the edge or end with a saw. Wane typically occurs on the ends of lumber but may also run anywhere across the board's length. Wane usually occurs on one side of the board only and typically doesn't affect the integrity of the lumber. In most applications the board can be used normally by turning it over to reveal the good side.