The base of support is the area by which the body is supported. For example, when you stand with your legs apart, the area under and between your feet is your base of support. If you hang from a parallel bar, your base of support is the area between the outer limits of your hands.
The larger the area of the base of support is, the greater the stability. For example, when doing the stork stand balance test, people are asked to balance on just the ball of one foot. With such a small base of support, it is difficult to maintain balance.
It is important to note, however, that a body may be stable in one direction but not in another. For this reason it is essential to consider the orientation of the base of support relative to the force being applied. For example, a wrestler wanting to prevent being Just having a wide stance with his feet side by side would not prevent the wrestler from losing balance backwards.