Limited Slip Differential. It basically equalizes the torque going to the driving wheels. Do a burnout or accelrate in a turn, youll notice the tC suffers from a bad "peg leg". Itll one wheel burnout like that. The basic way to think of it is, youre making both wheels turn with the same force, not one with alot and one with a little.
www.howstuffworks.com they can explain it better than i ever can