Timber that is cut parallel to the rays (the lines that run out from the center of the log) is termed "quarter-sawn." This means that the log is first cut into quarters, then each cut is made from the outer edge (bark area) towards the center of the tree. Wood that is cut perpendicular to the rays is termed, "flat-sawn" or "plain sawn".

Quarter-sawn wood is the strongest cut of wood that you can get, and it's specifically what we use in the construction of Taylor guitars.