Four-wheel drive, All-wheel drive, AWD, 4WD, or 4x4 ("four by four") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously. While many people associate the term with off-road vehicles and Sport utility vehicles, powering all four wheels provides better control than normal road cars on many surfaces, and is an important part in the sport of rallying.
In abbreviations such as 4×4, the first figure is normally the total number of wheels, and the second the number of powered wheels. (The numbers actually refer to axle-ends, which may have more than one wheel.) 4×2 means a four-wheel vehicle that transmits engine power to only two axle-ends: the front two in front-wheel drive or the rear two in rear-wheel drive. By this system, a six wheeled military transport truck would be a "6x6", while the typical American semi-truck tractor unit having two drive axles and a single unpowered steering axle would be a "6x4". In Europe it's not uncommon to see "6x2" trucks, with three axles, but only one of them is driven.
Read more about Four-wheel Drive: 4WD Versus AWD, 4WD Versus IWD, History, Road Racing, In Construction Equipment, Terminology, Unusual Systems, Introduction To Off-roaders, Introduction To Passenger Cars
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