You've probably seen "ghost marriage" in chinese movies.
Ghost marriage is called "Gui Hun 鬼婚" in chinese. Such marriage is also often called "Ming Hun 冥婚" or "Ying Hun 阴婚". It refers to marriage in the non-human realms, such as the underworld, the realm of ghosts, realm of hell etc.
Ghost marriage formed a part of the ancient chinese marriage practice that had its root dating from Pre-Qin era. In the Book of Rites 《周礼》, it was recorded “禁迁葬者，与嫁殇者。” (forbid the moving of the tombs/coffin of those who had passed away and died young, but getting marry). This implies that if a person had not married, but had died at an early age, he/she could still undergo a marriage ritual for him to 'get married in the underworld'.
The ancient chinese emphasized greatly on marriage when a person reached a certain age. In ancient times, a man will usually get married at 20 years old while a girl will get married at 15 years old. If he died without getting married, he would not enjoy the practice of worshipping/honoring by their relatives. In addition, if a person died young but had no partner, it would seem very sad for such a person. This is probably the origin of Ghost marriage
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