Caster Angle adjusts the angle of the suspension geometry forwards or backwards when viewed from the side angle of the car. Positive Caster Angle points the axis more rearwards at the top.
More positive Caster Angle will make the car more stable at high speeds and will increase camber gain with steering. It will also increase steering effort, making the car feel heavier and less responsive. Using a lower, positive Caster Angle will reduce both steering effort and jacking of the chassis with steering angle.
Pro Tip for wheel users: Increasing Caster Angle will make the steering feel heavier, but also greatly improve the feel at the front end of the car. Increase this as high as you can tolerate, ideally to max value.