Concubinage is the state of a woman or youth in an ongoing, quasi-matrimonial relationship with a man of higher social status. Typically, the man has an official wife in addition to one or more concubines. Concubines have limited rights of support from the man, and their offspring are publicly acknowledged as the man's children, albeit of lower status than children born by the official wife or wives.
In France, Concubinage is the official term for cohabitation of heterosexual and, since 1998, homosexual couples, and has none of the connotations that the English word has. Some benefits of married couples or those bound by PACS (civil union) may then apply.
(In jurisdictions with common-law marriage, cohabiting partners may become common-law spouses after a certain length of time.)