The magical power that permeates from the word that describes the "unknown". those who are mesmerized by that power.  These people were called the hunters. The hunter's job is to protect the order of mankind and nature.  Gon's journey begins so that he may become a hunter just like his father. And also so that he may find his father.  In order to become a qualified hunter one must pass an austere test.  It's said that only one in tens of thousands, one in hundreds of thousands pass the test.