What is the difference between AWD and 4WD?

AWD is a system that without driver intervention, shifts power between the rear and front wheels. This system is typically found on light-duty SUVs or passenger cars. The AWD drive system is designed for mild inclement weather conditions such as light snow, ice and rain. It is not designed for off-roading or severe weather conditions such as heavy snow or mud. This is where the 4WD system comes into the picture. 

4WD is a system that includes a transfer case that directly applies power to the rear axle, both front and rear axles and in some cases, only to the front axle. In addition, some 4WD systems include lower gear ratio options, locking hubs and lockers in the axles that force an equal amount of power to each wheel. All this taken together enables a 4WD system to enable a vehicle to navigate through deep snow, mud, over rocks and other obstacles with ease. The 4WD system is most commonly found on trucks, Jeeps and other purpose-built vehicles designed for heavy-duty use, whether for work or pleasure.