A divination tool originally developed from casting yarrow stems, the eight trigrams (八卦) represent every configuration possible from combining two types of line - broken and unbroken - in sets of three. In the cosmological terms of the Yi Jing, a unity (太極) engenders two opposing poles (兩億) [A/B], which in turn engenders four types (四象) [AA/AB/BA/BB]. This in turn engenders the eight trigrams (八卦). By combining two trigrams together, you have 64 hexagrams , each with meanings attached to aid with decision making.
The first of the 8 trigrams is represented by the character 震 zhèn, meaning 'to shake', but here representing thunder. It is associated with the Eastern point of the compass. In family terms, this trigram is associated with the eldest son.
The second trigram, 巽 (xun), represents "wind" or "wood", and Southeast on the compass. In the family, this trigram represents the eldest daughter.
The third trigram, represented by 離 (li), symbolises fire. This trigram correlates with the southern point of the compass and, in family terms, the middle daughter.
Three broken lines form the "Earth" trigram, represented by the character 坤 (kun). Corresponding to the southwesterly point of the compass, the trigram is associated with the mother of a family.
Represented by the character 兑 (dui), this trigram symbolises "marshes" and correlates with the western point of the compass. In the family, the 兑 trigram represents the youngest daughter.
This trigram consists of three unbroken lines and represents Heaven; a perfect counterpoint to the three broken lines of Earth. It is represented by the character 乾 (qian). On the compass, the trigram points to Northwest and, in family terms, it represents the father.
This trigram, represented by the character 坎 (kan) means "water". It correlates with the north point of the compass and in the family represents the middle son.
The final trigram is represented by the character 艮 (gen) and symbolises "mountains". This trigram correlates with the Northeastern point of the compass, and the youngest son in the family.