Let's say that you and Rosie O'donnell went on a date, you got back to your house and she jumps on your table. It will FLEX, if she quickly gets off, it will flex right back.
Now let's say that she decides that she loves your balls and starts playing with all 16 of them until she passes out. You find her the next morning, still in the center of the table.
That FLEX would have set in long enough to become permanent, and now you can say it's WARPED.
Same thing with a shaft, bend it and it will bend right back. Keep it in the bent position for a few weeks and you will have a warped shaft.