Wheel Slip

Torque is the twisting force that the engine produces.This is this torque force produced by the engine that moves the car. Maximum torque can be sent to the wheels in the 1st gear is the it has the maximum gear ratio.

Traction is the maximum amount of the force which a tire can apply on the ground.

Here is a simple demonstration which will show the importance of traction on a vehicles' performance.

{Taken from HowStuffworks)

There are two types of Wheel slip that occur. They are Static and Dynamic. In Static Wheel Slip the tire and road are not slipping relative to each other. The static wheel slip provides better traction. On the other hand the Dynamic wheel slip is the one i which there is relative slipping between the tire and the road., This gives a lower traction on road.

These wheel slip can be avoided in a 4WDS.