Our clients frequently ask about the grain patterns (figures) in wood.  The pic below explains how a log is milled:

For a light-hearted explanation, Stumpy Nubs, a woodworker, explains what a “Board Foot” measurement is.

Then there is grading of the wood itself: #1, #2, #3, etc.  #1 is knot-free.  #2 has a few knots.  #3 has more knots, and so on.

There is much more to discuss on this topic.

~ Peter