Swinging

1. A married person who practices mate-swapping.
2. Or: swinging-single , an unmarried person unhibited in his/her pursuit of pleasure, especially one who engages freely in sexual promiscuity.

Quote: Lawrence Paros in The Erotic Tongue (1984): ‘ Around 1953, a phenomenon called wife swapping was reported in the suburbs. During the early to mid-sixties, swinging couples or swingers became the subject of serious study by sociologists as well as a common male fantasy. But there was little need to limit swinging to married folks, and it expanded to include any kind of innovative sex with multiple partners, rendering all other definitions obsolete. The swinging-single was now upon us .’