Imperial Chinese harem system

The ranks of imperial consorts have varied over the course of Chinese history but remained important throughout owing to its prominence in the management of the inner court and in imperial succession, which ranked heirs according to the prominence of their mothers in addition to their birth order. Regardless of the age, however, it is common in English translation to simplify this hierarchy into the three ranks of empress, consorts, and concubines.

Source: Wikipedia — Imperial Chinese harem system (CC BY-SA 4.0)