Yin and Yang are represented symbolically by a broken line and a single solid line respectively.
If you take two Yang Lines, place it at the bottom and then add a Yang Line and a Yin line on top, you get a combination known as Greater Yang and Lesser Yin. Do the same with the Yin Lines and you get another two combination known as Greater Yin and Lesser Yang as shown below?
Finally if you add a Yin or a Yang line to each of the symbols generated above you get eight different sytnbols each known as a Kua.
Gua or Kua refers to the same thing. This is due to translation from the different Chinese dialect resulting in different pronounciation and spelling. A Kua is also frequently called Trigram.
Greater Yin Lesser Yang Lesser Yin Greater Yang
aa. ae rtkl «ea yuan tmssa y.rata
Kun Ken Kan Xun Zhen li wi Qhh
Notice that there are eight Kuas. Collectively they are known as Pa Kua or Eight Gua. It is also written
in many text as Ba Gua which means the same thing. In English it is known as the Eight Trigram. Each kua is given a name. They are Qian, Dui, Li, Zhen, Xun, Kan, Ken and Kun.
Like Yin Yang and the Five Elements, the Pa Kua is pervasive in Chinese Metaphysics and is reputedly invented by China’s first legendary emperor who live around 2800 BC!