Living together with several different sex/romantic partners. To have multiple girlfriends or wives, all of whom know about each other and live in the same
house. Polygamy.
Originated thousands of years ago as a means of producing a large number of offspring, and as a status symbol, to show off how many women and children a man could afford to provide for, and to display virility. Now banned in most countries, but was once
common practice,
even in early Christendom: Charlamagne had multiple wives.
The word was recently popularized by one Ricky Lackey, a convicted thief who, when asked by the judge at his trial how many children he had, replied: "None now, but I have
six on the
way." When the judge asked if he was marrying a
woman who had
six children, he replied "No, I be concubining." Meaning, of course, that he had 6 girlfriends, all of whom were pregnant.