A concubine is a woman who is not legally a wife but lives with a man and has a recognized position in his household. Ususally the man would seek out a concubine to satisfy his pleasures because his wife wasn't able to.
The term comes from the Latin prefix com-, which means "with," and cubara, "to lie down." Both the Ancient Greeks and Romans had concubines, and concubinage also appears in the Christian Bible. These...