What is the difference between AWD and 4WD?

All-wheel drive systems distribute power to all four wheels automatically and continuously, using electronics and differentials to shift torque where grip exists without driver input. They are tuned for on-road traction in rain, snow, and loose surfaces, and they are found in most crossovers and many sedans. Four-wheel drive traditionally means a more robust, driver-selectable system with a transfer case offering a low-range gear for crawling over rough terrain, towing, and steep grades, found in trucks and serious off-road vehicles. Older 4WD systems could not be used on dry pavement without binding the drivetrain, though many modern ones add an automatic mode that blurs the distinction considerably.

The safety point matters more than the terminology. Both systems help you accelerate and maintain traction; neither helps you brake or corner on ice, because stopping and turning depend on the grip of the tires against the road, not on how many wheels receive power. That mismatch is exactly why so many winter ditch incidents involve confident drivers of AWD SUVs, who gain the ability to get moving without gaining any ability to stop. Good winter tires do far more for cold-weather safety than a drivetrain upgrade, and a front-wheel-drive car on winter tires will generally outperform an all-wheel-drive vehicle on all-season rubber in the conditions that actually cause crashes.