What yin and yang mean
Yin and yang is a core idea of Chinese philosophy, especially Taoism: two opposite but complementary forces found in everything. Yin is dark, cool, soft and receptive; yang is bright, warm, firm and active. Neither is good or bad, and each turns into the other over time, like night and day.
The words first referred to the shady and sunny sides of a hill. The black-and-white circle is called the taijitu, the diagram of the supreme ultimate. The black half is yin, the white half is yang, and the small dot of the opposite color inside each half shows that each side always holds a seed of the other.
Trigrams and the I Ching
Write a yang line as ⚊ and a yin line as ⚋, stack them three at a time, and you get the eight trigrams of the I Ching (Book of Changes), the bagua: heaven ☰, lake ☱, fire ☲, thunder ☳, wind ☴, water ☵, mountain ☶ and earth ☷. Pairs of trigrams make the 64 hexagrams, which Unicode also includes, from ䷀ to ䷿.
You can see the taijitu and four of the trigrams on the flag of South Korea, where a red and blue circle is surrounded by ☰ ☷ ☵ and ☲.
How to type the yin yang symbol
In Microsoft Word, type 262F and press Alt + X. In HTML, use ☯. On a Mac, press Control + Command + Space and search "yin yang". On iPhone and Android, search "yin yang" in the emoji keyboard to get ☯️.
The half-black circles ◐ ◑ look similar but are geometric shapes, not the yin yang symbol. For calm, balanced bios, ☯︎ pairs well with ☮︎ from the peace symbol page or the phases on the moon symbol page.