4 wheel Electronic Traction System
Working with the vehicle's full-time four-wheel drive, 4-ETS uses individual wheel-speed sensors to detect the onset of wheel slip. Then it individually brakes the slipping wheels as needed, providing the effect of locking the front, center and/or rear differentials. The 4-ETS system continually balances the torque split to direct power to the wheel or wheels with traction.

4 Wheel Drive and Automatic
4MATIC is the name of a complex electronically controlled all wheel drive system developed and used by Mercedes-Benz on some of its models. All Mercedes cars featuring this system also have an automatic transmission in standard equipment and that's where its name is derived from (4-wheel drive and automatic transmission).

Originally developed together by Mercedes and Steyr-Daimler-Puch engineers, the system is now at its third generation but it's still based on a rear wheel drive chassis on most of the models. The system employs locking central and rear differentials to provide additional traction in slippery conditions or during off-roading. On the G-Klasse the system uses three locking differentials (front, central and rear).

Four Wheel Drive
Four Wheel Drive is a system which transfers engine power to four wheels independently and is mostly found on SUVs and all-terain vehicles. By using differentials it can transfer almost any amount of power percentage to any of the four driving wheels.
Two Wheel Drive
This expression is used to describe a vehicle with only two wheel drive. The first figure is the total number of wheels, and the second is the number of driving wheels. In some countries it's essentially a different name for rear-wheel drive vehicles (RWD), unlike 2X4, which can be used for describing a front-wheel drive vehicle (FWD).