Concubine

Concubines are women engaged in interpersonal relationships with a man without being married to him, or at least not to the fullest extent of marriage, such that their position is inferior to that of a primary lover. The relationship often involves cohabitation and sexual activity. In polygamous societies, they may be legally married but bear a lower rank than of the main wife.

In China, it was common practice for prestigious men to have several concubines. For that reason, the Emperor of China usually had thousands, each who were ranked according to a strict hierarchy.

History
By the time of the Ming dynasty, concubinage was a millennia-old tradition, and the consorts of the emperor were governed by a standardized ranking system. Highest of the consorts was the empress, and only she held the official status of wife to the emperor. Only heirs of the empress had the right to be designated crown prince. Despite her prestigious position, concubines of lower rank could potentially climb the hierarchy and succeed her, in which event, she was deposed. Even the most influential concubines paled before the power of the emperor, who had the authority to order their executions on a whim.

Below the empress were the Imperial Noble Consorts, followed by the Noble Consorts, Consorts, and Imperial Concubines. As ladies of the court, the concubines were taught the finer arts of music, dance, singing, literature, and embroidery. As was the custom at the time, their feet and breasts were often bound to conform with popular conceptions of beauty, though concubines prized for their dancing such as Shao Jun were spared from this practice.

Reference

 * Assassin's Creed Chronicles: China