And one new definition - underlying surface (surface in its original state).
Another fundamental definition - trim curve (http://moi3d.com/wiki/FAQ)

In another words ShrinkTrimmedSrf command reduce size of initial state of surface, make it fit to your trim.


Michael I think this definition have to be on the first place in tutorial list) Because it's how nurbs works on low level.
Now knowing this, I am sure I'm more confident in nurbs modeling.
It's peaty a bit that I know it accidentally after half of year of using MOI :)