All-Wheel Drive (AWD), or four-wheel drive, is a propulsion system that sends power to all four wheels of a vehicle instead of the traditional two-wheel drive. This type of system was originally developed for off-road vehicles, but in recent years it has become increasingly common on road vehicles.

All-wheel drive offers several advantages over front-wheel or rear-wheel drive vehicles. First, it provides greater traction and grip on the road, especially in adverse weather conditions such as rain, snow, or ice. Second, it improves the stability of the vehicle in curves, providing greater safety for the driver and passengers. Finally, all-wheel drive can improve the vehicle's performance by offering better acceleration and greater towing capacity.

There are two main types of all-wheel drive: permanent all-wheel drive and on-demand all-wheel drive. Permanent all-wheel drive, as the name suggests, continuously sends power to all four wheels regardless of road conditions. This system is often used on off-road vehicles and SUVs.

On-demand all-wheel drive, on the other hand, sends power to all four wheels only when necessary. The system constantly monitors road conditions and, if it detects a loss of traction on one or more wheels, sends power to the wheels with greater grip to restore traction. This type of all-wheel drive is often used on luxury and sports road vehicles.

While all-wheel drive offers numerous advantages, there are also some disadvantages to consider. First, all-wheel drive vehicles are generally more expensive than front-wheel or rear-wheel drive vehicles. Second, the all-wheel drive system requires more maintenance and can be more difficult to repair in case of malfunctions. Finally, all-wheel drive vehicles tend to have a higher fuel consumption than front-wheel or rear-wheel drive vehicles.

Overall, all-wheel drive is a highly efficient propulsion system that provides greater traction and grip on the road, improves stability and vehicle performance. However, as with any technology, there are also some disadvantages to consider. Before purchasing an all-wheel drive vehicle, it is important to assess your driving needs and requirements to determine if this propulsion system is right for you.