The yin-yang is a symbol representing the relationship between
yin and
yang. It looks something like this:
.d8888888888b.
.d8P 888888888b.
.dP d888888888888b.
.dP d888888888888888b.
.dP d88888P Y888888b.
.dP d888888 8888888b.
.dP 8888888 88888888b.
8P 8888888 8888888888
dP Y888888b d8888888888b
88 Y8888888888888888888888
88 Y888888888888888888888
88 Y88888888888888888888
88 Y88888888888888888
88 Y888888888888888
88 Y88888888888888
88 d88b Y8888888888888
9b d8888b 888888888888P
Vb 888888 888888888888
`Vb 98888P 8888888888P'
`Vb 988P 888888888P'
`Vb d88888888P'
`Vb d88888888P'
`Vb d8888888P'
`V8b d88888888P'
`98888888888P'
The dark portion represents yin, while the light portion represents yang. The small circle of yin within yang represents how yin is present in the very core of yang. Likewise, the small circle of yang within yin represents how yang is present in the very core of yin.
This symbol is also known as the Tao or the Tai Chi.