What does it mean to have a superficialization of my fistula done?

Make easy to stick. If your fistula is too deep, your surgeon can move vein closer to the skin so that it is easier to access.
Closer to skin. This is to bring the vein which the dialysis nurses are trying to "needle" / access closer to the skin. Sometimes the vein itself is robust and the blood flow is adequate, but because of its depth the nurses have a hard time getting the access needles in. This will cause "infiltrations" or bleeding around the vein. A simple solution is to surgically bring the vein closer to the skin.