When people speak of the "flat spot", they are referring to the way bottom of the downswing, right before release of the bowling ball. Ideally, a bowler would want as large of a flat spot as possible, but it is something which is hard to duplicate shot after shot.
If you were to take a video clip from the ride view (preferably the same side as your bowling arm), and in slow motion watch the clip towards the bottom of the swing, you will see that at a spot close to where your feet are, there is a flat spot where your arm swing is no longer moving in a circular pattern, it moves in a straight line. Programs like Ebonite Bowlers Map has a built in thing to trace flat spots, so if you ever get a chance to take a lesson with this software, take advantage of it.
--------------------
"Strike for show, spare for dough"
Im A Hammer Head 100%
http://ryman624.googlepages.com