Taiji (Tài Jí) is a foundational concept in Chinese philosophy, literally meaning 'Supreme Ultimate' — 'tài' conveys 'supreme' or 'utmost,' while 'jí' means 'extreme' or 'apex.' Together, they represent the primordial, undifferentiated source from which yin and yang emerge and interplay. It symbolizes the dynamic unity underlying all existence, not a static entity but the origin of cosmic balance and transformation.

In modern usage, 'Taiji' most commonly refers to Taijiquan (Tai Chi), the gentle, flowing martial art rooted in these philosophical principles. Practitioners use slow, deliberate movements to cultivate qi (vital energy), balance, and mental focus. The term also appears in traditional Chinese medicine, cosmology, and classical texts like the Yijing (I Ching), where it signifies the fundamental state before duality arises.