A measure of the force exerted on a surface by a vehicle as the result of gravity, expressed in terms of lbs/inch2 or kg/cm2. This is useful in determining what types of terrain a vehicle is able to pass over. Despite the fact that a tank, for example, weighs far more than the average car (up to 75 times more!) it usually has lower ground pressure, which enables it to travel over softer terrains such as marsh or sand without becoming bogged down. This is because the tank's weight is spread over the large surface area of the lower surface of its treads, whereas the car's weight is supported by the contact patches of its four tires, an area which is quite small. Since the ratio of these patches to the area presented by a tank tread is actually much smaller than 1/75 (or the ratio of the weights of our notional car and tank) the tank has better terrain characteristics due to its lower ground pressure.

Note that this says nothing about the weight of the vehicle! Ergo, a tank still shouldn't take a bridge that holds cars without checking to see if it can safely do so...