According to Wikipedia: Swinging, is also known as wife swapping or partner swapping, and is a non-monogamous behavior where both singles and partners in a committed relationship engage in sexual activities with others as a recreational or social activity. Other terms sometimes encountered are wife sharing, partner sharing, wife trading and wife lending, which describe similar concepts, usually in sociological or anthropological research. As these terms have become dated, with women participating as fully in the decision making process as their male partners, the more gender-neutral term "swinging" has gained popularity.
People may choose a swinging lifestyle for a variety of reasons. Many cite the increased quality, quantity and frequency of sex. Some people may engage in swinging to add variety into their otherwise conventional sex lives or due to their curiosity. Some couples see swinging as a healthy outlet and means to strengthen their relationship. Others regard such activities as merely a social and recreational interaction with others.
Source: Chaniapost