Open refers to the state of being peng. Peng can be described as a rounded, arched form that is exhibited in every part of the body. This roundness produces an equalized pressure in all directions: back and front, and side to side-similar to that found with a basketball. Think of each part of the body and the body as a whole as an inflated ball with equalized pressure going out from all sides and coming in from all sides.
Peng gives great strength to the body, making it, in a way, invincible. The roundness and openness is held, not with force, power, or strength. Peng is held with looseness from which comes agility, flexibility and strength.
Peng is held with looseness and openness at the same time. Peng cannot be stiff or hard, nor can it be closed or cinched. The openness in peng is held with looseness.