Hou (Chinese: 后; pinyin: Hòu) is a tile for ancient Chinese ruler, which may equivalent to King/Queen or Emperor/Empress.
The Chinese character Hou(后) is an ideogrammic compounds, in oracle bone script it is written the same as Si(司, means "to rule") as the combination of mouth(口) and hand(手). Hou usually refers to female rulers in oracle bone script. In Xia Dynasty, the title for Kings of Xia are Hou, for example the expression Xia Hou Shi(夏后氏) means King of Xia, and the contemporary leader Houyi. Kings of Shang Dynasty have their own title Wang, and Hou turned to refer Queen, the wife of King. This may reflect that rulers are female in very ancient times.
References
Hou (title) Wikipedia(Text) CC BY-SA