Four-wheel Drive (or 4WD)
A car with selectable four-wheel drive. So, a car in two-wheel drive under normal conditions, with the option of selecting four-wheel drive for certain situations. 4WD usually refers to “off road” vehicles that have selectable four-wheel drive for slippery conditions.
Four-wheel drive is more expensive to produce than its two-wheel drive equivalent and also adds weight to the car. Running costs are generally higher with four wheel drive vehicles.