The jianghu is the milieu, environment, or sub-community, often fictional, in which many Chinese wuxia stories are set.
In modern Chinese culture, jianghu is commonly accepted as an alternative universe coexisting with the actual historical one in which the context of the wuxia genre was set. Each wuxia novel has its own jianghu setting, although in Louis Cha's Condor Trilogy it will be one with continuity; whereas Gu Long's jianghu would be distinct in every novel.
The concept of jianghu can be traced to the 14th century novel Water Margin, in which a band of noble outlaws, who mounted regular sorties in an attempt to right the wrongs of corrupt officials, retreated to their hideout. These bandits were called the Chivalrous men of the Green Forests (simplified Chinese: 绿林好汉; traditional Chinese: 綠林好漢; pinyin: lǜlín hǎohàn). The "green forest" was the antecedent to jianghu.
One of the earliest coinage of jianghu was by a dejected poet Fan Zhongyan (989—1052) in the Song Dynasty in his poem Yueyang Lou Ji (岳阳楼记), in which the context of jianghu was set out as distant to the courts and temples, meaning a world in its own right.
Read more about Jianghu: Premises in Jianghu, Morality in Jianghu, Xia, Wulin, Modern Use of "jianghu"