4x4 =4WD

4WD vs 4x4: these terms are used interchangeably by automobile manufacturers. This term implies the car has a locking center differential. Which means that, when locked, the front and rear axles turn at the same speed. This is not desireable on high-traction surfaces (e.g. dry pavement), but very useful on low-traction surfaces (off-road, snow, etc.)