All-wheel drive

An all-wheel drive vehicle (AWD vehicle) is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand.

The most common forms of all-wheel drive are:

1x1

All unicycles
Reflects one axle with one wheel capable of being powered.

2x2

Some motorcycles and bikes
Reflects two axles with one wheel on each capable of being powered.

4×4 (also, four-wheel drive or 4WD)

Reflects two axles with both wheels on each capable of being powered.

6×6 (also, six-wheel drive or 6WD)

Reflects three axles with both wheels on each capable of being powered.

8×8 (also, eight-wheel drive or 8WD)

Reflects four axles with both wheels on each capable of being powered.

Vehicles may be either part-time all-wheel drive or full-time:

On-demand or Part-time

One axle is permanently connected to the drive, the other is connected as needed

Full-time or Permanent

All axles are permanently connected, with or without a differential.

Independent

The wheels are driven, but not dependent on a central mechanical power coupling.