Zhen

阵 (Zhen), or more specifically 法阵 (Fazhen), is a type of magic only mentioned in Chinese mythology and fantasy works. Although there are some sort of similar words in Chinese religions, especially in Taoism, those words are implied to some religion rituals instead of the deadly magic shown in the movie.

Originally, the word "Zhen" was used to imply the military knowledge about how to arrang and dispatch troop formations in the battlefield. However, since Chinese traditional culture often mixed military knowledge and occultism together, people tended to believe that there was a certain mysterious power in the formations.

Later on, folktales and fiction writers adapted this idea and claimed that people could create a magic zone by arranging special objects or symbols into a specific pattern. And this magic zone is called "Zhen" (in occult term). In those stories, a Zhen was usually used for trapping or kiling those who walk into it, so in a manner of speaking, it was a magic trap. And like a normal trap, it was generally discribed as an automatic system, but some folktales also believed that it could also be controlled from outside.

Escaping from a Zhen
In fiction stories, the knowledge about creating Zhen was a part of a complicated Chinese occult system called "Qimen Dunjia"(Mysteries, Gates and Hidden Things). It was a widely used for divination and many other different purposes. And since it contained the knowledge of creating a Zhen, it also offered a method to survive in a Zhen and even escape from it.

This method was called "Eight Gates". In general speaking, it was a way to "decode" the Zhen and find a safe area to stay. Since a Zhen was relied on putting special objects or symbols into a right pattern, a person could figure out the working principle of a Zhen by observing the pattern of those signs. After understanding its working principle, he could predicted the dangers he would face with the knowledge in Qimen Dunjia. According to those fiction stories, there were eight different fates when a victim was moving in a Zhen ("Opening/start", "Rest", "Life", "Injury", "Block", "Flourish", "Death", and "Shock"), and the directions led to those fates were called "Gates". Among eight directions, only the "Gate of Life" led to a safe zone, hence it was also called the "Gate of Survival". In the movie, Xu Xuan used this skill to locate the safe zone and saved Xiao-Bai twice.