Yin and Yang is one of the fundamental symbols of Chinese philosophy.
It refers to the two opposed and complementary principles that characterize the world, for example: good and evil, shadow and light, visible and invisible, material and spiritual, oneself and others …
This duality guarantees the harmony and balance of the universe.
The Yin as a part of Yang and the Yang as a part of Yin as well , they are inseparable.
The Yin is the black part of the symbol and represents the feminine, the night, the moon, the cold, the rest, the immobility and the unconscious.
The Yang, the white part of the symbol and represents the masculine, the energy, the day, the sun, the summer, the warmth, the mobility, the conscious.
Arasia-Shop offers a selection of yin yang products: hangings, rings, incense doors, necklaces … Take a look here
To go further: The五行 Wǔ Xíng or the Five elements here