The cohabiting of a man and a woman who are not legally married; the state of being a concubine. Note: In some countries, concubinage is marriage of an inferior kind, or performed with less solemnity than a true or formal marriage; or marriage with a woman of inferior condition, to whom the husband does not convey his rank or quality. Under Roman law, it was the living of a man and woman in sexual relations without marriage, but in conformity with local law.