Four-wheel drive, All-wheel drive, AWD, 4WD, or 4×4 ("four by four") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine.
In abbreviations such as 4×4, the first figure is normally the total wheels (more precisely, axle ends, which may have multiple wheels), and the second, the number that are powered. Syntactically, 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.
All wheel drive (AWD) refers to a drive train system that includes a differential between the front and rear drive shafts. This is normally coupled with some sort of anti-slip technology that will allow differentials to spin at different speeds, but still maintain the ability to transfer torque from one wheel in case of loss of traction at that wheel.