Yin-Yang Symbol of Duality

The concept of yin and yang (Traditional Chinese: 陰陽; Simplified Chinese: 阴阳; pinyin: yīnyáng) originates in ancient Chinese philosophy and metaphysics, which describes two primal opposing but complementary forces found in all things in the universe. Yin, the darker element, is passive, dark, feminine, downward-seeking, and corresponds to the night; yang, the brighter element, is active, light, masculine, upward-seeking and corresponds to the day.

The pair probably goes back to ancient agrarian religion; it exists in Confucianism, and it is prominent in Taoism, though the words yin and yang only appear once in the Tao Te Ching.

Yin and yang are complementary opposites rather than absolutes. Most forces in nature can be broken down into its respective yin and yang states, and the two are usually in movement rather than held in absolute stasis.

Extracted from Wikipedia, Yin and Yang