Backlash:
Where your drive shaft comes into the diff case. How much slop that has in it is the backlash. Hold the outdrives or diff gear and wiggle the center drive shaft without a motor in it. That is the backlash. You can adjust that with shims by moving the diff gear closer or further away from the bevel gear.
I don't remember how much there is with the stock shims, just a adjustment I got use to checking with the TC3.