Understand wood distortions...

In a previous post I mentioned that I did not know the correct term to describe a specific distortion in wood. So I have been doing some reading research.
So far I have found that wood will distort in four principal ways. These would be the four general ways of describing boards which are not flat.

In these pictures, the distortions are shown, in comparison to a normal flat board.

• Bow - the board curves in it's length, around the wider side.
  

• Cup - the board is curved in it's width, whilst it stays flat in it's length.

• Spring - again, the board is flat but is curved in it's length, this time it curves around the thinner edge.
  

• Twist - the board twists up in opposite directions around the ends.