Positraction and limited-slip are both types of automotive differentials. Differentials are located in the center of the front axle, center of the rear axle or, in some cases, both.
Differentials are designed to assist tires in turning at different speeds. When making a turn, one tire has to turn sharper than the other on the same axle to complete the turn.
The differential compensates for the differences in the tire angle during the turn. This allows the tire to maintain power through the turn.