It is this caster that keeps the bicycle wheel straight when we let go of the handlebars. Similarly, supermarket carts also have caster wheels on them to help them to retain direction when being pushed around. However, supermarket carts have the caster the other way around. In a vehicle, caster is generally built into the front wheels to keep the front wheels from wandering around while driving, and it is also caster angle that helps the steering wheel to return to centre after a turn. Caster is measured in degrees off the perpendicular, and a positive caster indicates the wheel is forward inclined, while negative caster is indicative of a wheel that is rear inclined.
Most cars have positive caster.
It is important that caster on both the left and right wheels should be equal, failing which the vehicle tends to pull to one side during acceleration and the other during deceleration. Again, caster adjustment is possible only on the more expensive vehicles, and even then not on all of them. As I know it, there are only a handful of models of the cars assembled in this country that has this built in adjustment. They must be in harmony with each other, failing which your vehicle is never at its' peak capability. Correct toe adjustment with wrong camber will not work, neither will correct camber with the wrong toe.