Or do you maybe mean the "seam" curve of a closed surface?

When you do a revolve, it creates a closed surface - every NURBS surface has a rectangular layout to it and to make a closed surface it's kind of like taking a piece of paper and rolling it up so that 2 edges touch each other. That touching edge area is called the "seam" edge of the closed surface.

When doing fillets, it can be possible for the seam edge (or any edge) to mess up filleting since a fillet will not cross over some other nearby edge that is not actually part of the current fillet set.

If that's what you are running into you may need to do something like rotate the revolve by 90 or 180 degrees to get its seam edge out of the general area where you are trying to do the fillet.

- Michael