Concubinatus

A concubinatus (Latin for "concubinage" – see also concubina, "concubine", considered less pejorative than paelex, and concubinus, "man who lives with another with no legal marriage") was an institution of quasi-marriage between Roman citizens who for various reasons did not want to enter into a full marriage or faced legal obstacles to doing so. The institution was often found in couples when one partner belonged to a higher social class or where one of the two was freed and the other one was freeborn. However, it differed from a contubernium, where at least one of the partners was a slave.