It is important for you to know that not all the wheels of your car spin at the same speed when it is moving. This is because the inside of the wheels needs to travel a shorter distance than the outside wheels need to during the turning. This is so both in front as well as rear wheels.
Open slip differential
This poses a problem because the wheels that receive power from the engine and spin are designed to turn the same way. It is the differential (a set of gears) overcomes this problem by transferring torque to both the wheels and at the same time allowing them to rotate at different speeds. The differential commonly used in two wheel drive vehicles is open slip differential.
This design of enabling the wheels to spin at different speeds functions very well at surfaces which have good amount of traction, but in surfaces like ice or lose gravel, they have crucial disadvantages. Imagine one of the driving wheels of a vehicle moving over a patch of snow, and the others moving over a normal surface. In such a situation, the differential would direct all the torque towards the wheel that offers the least resistance, and in this case, the wheel is moving on snow. Thus, one of the wheels gets more torque than needed and this results in slippage. Getting back to normal movement in such cases would not be possible until both of the wheels start to get enough traction from the surface.
To enable the rear and the front axle spin at different speeds, a differential is introduced in between them, in addition to the two right-left differentials already present. Thus, drive train binding is avoided. But there is still the problem caused by the nature of open differential. That is, the slippage caused by the differential putting extra torque on the wheel offering least resistance.
However, both four-wheel drive and all wheel drive, overcome such problems by other kinds of differentials or devices that prevent from slippage.
Limited slip differential
Limited slip differentials are very much like open differentials, in that they allow for wheels to spin at varying speeds. Limited slip differentials have a spring pack and a set of clutches. When the wheels move in a straight line, there is no real use of the clutch. When there is a requirement for one wheel to spin faster than the other, the clutches come into action. For the wheels to spin at varying speeds, they must first overpower the clutch. When in a snow patch, if on wheel tries to spin faster than the other, the clutch would try to disallow it. The physical strength of the spring and the friction induced by the clutch determine how much force is needed for the wheel to spin at differing speeds. In a condition like snow, the clutch would overpower differential rotation of any wheel, because there is not much pressure on the clutch and the spring. But in conditions like taking a turn, due to the traction offered by the surface, the wheels overcome he clutch and spin at different speeds.
