Short answers, pulled from the story.
Concubinage means the state of cohabiting in intimacy without legal marriage. The English term appeared in the late 14th century, derived from Latin through Old French; the Latin root concubinatus described a permanent cohabitation in ancient Rome, and the verb concumbere means "to lie together."
In premodern China, successful men could have multiple concubines while being limited to one wife; the number of concubines permitted was set by law and tied to the man's rank, from the Eastern Han period (AD 25-220) onward. Concubines were purchased similarly to slaves but held higher status, brought no dowry, and could not remarry after their master's death. The Chinese Communist Party outlawed concubinage when it came to power in 1949.
Lady Yehenara, known as Empress Dowager Cixi, entered the Qing imperial court as a concubine to the Xianfeng Emperor and gave birth to his only surviving son, who became the Tongzhi Emperor. After her husband's death she became the de facto ruler of Qing China for 47 years.
Ottoman sultans generally preferred concubinage to marriage, and for a time all royal children were born of concubines. Sultans appeared to limit themselves to one son per concubine, ceasing intercourse once a concubine bore a son, which constrained the political influence of any one son. Leslie Peirce argues this was because a concubine lacked the political leverage of a princess or local elite daughter.
Plaçage was a formalized system of concubinage that developed in Louisiana and former French territories. European men took enslaved or free women of color as mistresses after arranging a dowry, house, or property transfer, sometimes including freedom and education for their children. This produced a distinct class of free people of color in New Orleans whose descendants are generally known today as Louisiana Creole people.
Switzerland still uses the term as of 2025 as a legal status for cohabitation without marriage. France formalized an equivalent in 1999 as its version of a civil union. The United States once used the term in law for cohabitation but the concept never evolved and is now considered outdated.