Concubinage
Concubinage is the state where a young women is in an on-going quasi-matrimonal relationship, meaning that this women has a "somewhat marriage" with a man of higher class. That man would have in addition to one or more concubines, an official wife. The man would not provide full support to his concubine(s), and any children from them would be publically acknowledged as his, and would be of lower status than the children he has from his official wife.
Historically, concubinage was usually voluntary, by the women or her family, since it provided economic security for the women. Involuntary concubinage involved sexual slavery of the woman.
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