Many people use the terms “all-wheel drive (AWD)” and “four-wheel drive (4WD)” interchangeably. While the basics of the systems may be similar, they are constructed differently and with different uses in mind. AWD drivetrains feature front, rear, and center differentials that send power to all four wheels of the vehicle and are typically found on smaller cars or crossovers to be used as a performance booster. Vehicles with a 4WD drivetrain employ two differentials and a transfer case to provide power to all four wheels of the vehicle. Both AWD and 4WD systems help vehicles maintain traction in slippery and inclement weather conditions. AWD has typically been for sporty cars on pavement and typically come in two styles: part-time and full-time AWD. Some AWD systems offer torque vectoring, which uses sensors to direct engine power to the wheels that have the most traction at any given time, no matter where they are located on the vehicle.
A word of caution first. Manufacturers tend to obscure the true nature of their 4WD/AWD systems behind phantasy names like "Active 4WD", "Quadra-Drive", etc. - others might call their automatic AWD "Real Time 4WD".
There is plenty of confusion about what is what. Does it matter? Can't you just call "four wheel drive" "all wheel drive"? Yes you could. If all eight wheels of your big truck are driven, isn't it all wheel drive? Yes it is.
However, there are so many different 4WD systems on the market now that it is important to be precise and specific. It is important to call AWD when it is AWD and full time 4WD when it is full time 4WD. Just to say 4x4 is not sufficient any longer.
Wrong terms lead to misinformation - intentional or not. Wrong terms might make you buy something you neither want nor need! Do your homework before buying a 4WD - to get what you really need.
There is no sanctioning body who ever established the definition of terms regarding 4x4. The terms used below are the ones used internationally by engineers and competent magazines.
system is the newest kid on the block. PR agency generated names like "Real Time 4WD", "intelligent AWD" or "active AWD" are hiding the fact that automatic AWD is essentially a sophisticated 2WD system. Automatic AWD is NOT powering all 4 wheels all the time. Only on rare occasions all 4 wheels will be powered very briefly. Since AWD is only engaged on rare occasions, sometimes automatic AWD is falsely called "part time 4WD". Engineers refer to this system as an "on demand system". Since it is based on an existing 2WD steup, it is also referred to as a "hang on" solution.