It's the lateral left (for right handers) shift. I call it “the bump” for short. At our recent tournament we had supervised practice and a morning clinic and there were many questions about “the bump,” like how far do you shift.
A number of players were going too far, some as much as five inches, which caused all sorts of problems. The correct answer is no more than one and a half inches — or less. Use your belt buckle as a measurement. It shouldn't shift more than one and a half inches forward.
I think this video will help out greatly. Check out the door jam drill. It's really that easy. Get the feel for how little you move. Our narrower stance makes it easy to shift your weight from back to front. The key is: don't over do it.