Central Equilibrium (中定) from Tai Chi Chuan Teaching Notes (太極拳講義)

中定

伸屈開合之未發謂之中，寂然不動謂之定。心氣清和，精神貫頂，不偏不倚，是為中定之氣，亦道之本也。

吳公藻

"Before the action of extending, bending, opening and closing is called center. Silent and still is called equilibrium. The Xin and Qi are clean and harmonious, the spirit of vitality reaches the top of the head, no tilting, no leaning is called the Qi of Central Equilibrium. It is also the root of the Dao."

By Wú Gōngzǎo (吳公藻), based on the translation by by Yang Jwing Ming (楊俊敏) presented in the book Tai Chi Secrets of the Wu Style (太極拳吳氏先哲秘要).