Ghost Gate--Guimen Gate

Ghost Gate in Chinese traditional operas, also called Guimen Gate, was a parlance for stage setting in the Song (960-1279) and Yuan (1279-1368) Dynasties. It then referred to the door that connected the stage and the background.
It is said that the roles operatic performers played were mainly of ancient men, some of whom were long gone, so the door that the long-gone "ghosts" passed through was called the Ghost Gate.