PiGua can be variously translated as Split-Deflect or Ax-Hitch Boxing. In the old days this was a form of Kung Fu used when warriors wore armor. The very famous Ming general Ch’i Chi-Kuang (Qi Jiguang) in his book New Essays on Martial Arts the act of fighting while armor-clad.

A contemporary PiGua book
In 1928 when the well known and influential National Wushu Institute was formed a PiGua master of repute, Ma YingTu, was put in charge of the entire operation. One of his first acts was to invite Guo Changsheng, another PiGua practitioner from Hebei, to lecture at the institute. Together they did one of the first restructurings of Wushu not only streamlining the style, adding power moves but taking as inspiration the ancient actions of 24 Movement TongBei Chuan (Through the Back Fist). Much of the PiGua now popular came from the efforts of these two men and the revised version they created. However much traditionally structured PiGua remains.
In Gansu province Pi Gua practices some of the following fists:
PiGuaJia
Blue Dragon
Flying Tiger
DaChiaTau Chuan (Dajiazi)-Big Frame Fist
TaiShu Chuan
In the world famous Tsang (Cang) County, the home of many great boxers, we have
PiGua Zhang
Green Dragon (absorbed into Pigua but might have risen as a form separate form originally)
Slow and Fast PiGua
Canon Boxing
PiGua concentrates on movements which are complimentary, actions that reinforce one another. A good PiGua demonstrator exhibits accuracy, fluency, agility, continuity, speed, power, subtlety and ingenuity. PiGua players are known for slow stance work but very fast hand motions. Arm strikes arrive from highly unusual angles often tracking to a “return” flight to reach their targets. The Key Words of the style include
Strangling
Tumbling
Splitting
Deflecting
Chopping
Scissoring
Picking
Brushing
Discarding
Stretching
Withdrawing
Probing
Feeling
Flicking
Hammering
Beating
PiGua, also known as Long-Armed Ape Style, is truly unique in execution. The arms are move with such extreme looseness that practitioners often seem to have no bones. (In fact, for emphasis, many performers were their sleeves extra long to heighten the effect. Because of this PiGua is particularly appropriate to female players with high flexibility). PiGua is a popular style in China and sometimes mixed with other forms. The most famous marriage is that of PiGua and BaJi two styles which really seems to compliment each other. And, indeed, there are bridge forms such as PiGua/BaJi first which cross both styles. PiGua, due to its loose arm flapping and extremely sinuous appearance is often said to resemble the animal actions of the Snake and the Eagle.
Resources:
PiGua is a great style but with few videos or books in English. Here are some to check out…
PiGua Structure-DVD and PiGua Palms-DVD by Adam Hsu
Pi Gua Miao Dao Knife
Pigua VCDs with Guo Rui Xiang
Gansu Boxing style PiGua
More PiGua VCDs