yin-yang

yin-yang (yēn-yäng),

n governing theory behind traditional Chinese medicine; the idea that life is filled with opposite yet complementary characteristics and qualities on the physical and spiritual levels and on the macro and micro levels. The concept is that each entity can be essentially itself and its opposite; additionally, yang's seed is believed to be contained within yin. A balance of yin and yang is considered essential for good health, whereas a deficiency or imbalance in either factor can manifest as disease.

Yin-yang.