Overview
Sing-song girls, also known as flower girls, is an English-language term for the courtesans in China during the 19th century AD.
Origin
Before the founding of modern China in 1911, concubinage was legal. In Chinese custom, males carry the family name and the family's heritage after marriage. To ensure male heirs were produced, it was a common practice for an upper-class married male to have one or more concubines, provided he could support them.
The custom could be invoked without the wife's consent: the husband's actions were protected by law. Concubines would co-exist in the family along with wives and children. A man might choose a courtesan to be his concubine. Many of these courtesans would sing songs to attract potential husbands, hoping to become secondary wives.
Terminology
Western observers in China during the nineteenth century witnessed these women singing but had no idea what to call them since they were not classified as prostitutes. Thus the term "Sing-Song Girls" came about.
From Wikipedia (CC BY-SA 4.0).