What is a Slipperential?

[RC-Monster Mike]

Correct. The diff cup has 2 end caps - one for the "slipper" side, which is built first. The diff is built from the other side, so diff maintenance/fluid changes can be made without touching the slipper settings.
The aluminum rod sticking out of the adjustment nut is used to adjust the slipper setting while it is installed in the car(threads into the nut for adjustment).