terminology

hitting the ball thin means you hit the ball half way up with the leading edge/bottom of the club, hitting it fat means you hit the ground before you hit the ball
 
A thin shot will usually go low and long, a fat will pop up and hardly go anywhere.

Last round I hit a 4 iron thin onto a green from 180 yards out and I hit a 56* wedge fat about 5 yards!
 
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