Green’s Dictionary of Slang

swinging n.2

[swing v. (8g)]

indulging in husband-and-wife swapping parties; thus closed swinging, swapping parties in which only husband-and-wife partnerships take part, no singles are allowed to unbalance the situation; as opposed to open swinging, in which all-comers – married or single – are welcome and all end up in the same bed.

[US]L. Bruce Essential Lenny Bruce 88: Our smut factories have been working for years — hot books and swinging and everything.
[US] ‘The Amer. Way of Swinging’ Time 8 Feb. 36: ‘Swinging,’ an activity defined as ‘having sexual relations as a couple with at least one other individual’.
J.L. McCary Freedom and Growth in Marriage 86: Couples who opt for mate-swapping or swinging as a viable alternative to sexual exclusiveness in monogamous marriage give as their reason [etc.].
[US]personal ad, restroom Murray & Murrell Lang. Sadomasochism (1989) 52: Partner(s) wanted for light S and M, closed swinging.
[US]personal ad, adult bookstoreMurray & Murrell Lang. Sadomasochism (1989) 100: Bored housewife needs a little excitement! Would like to get into open swinging.
[US]Chapple & Talbot Burning Desires 15: Swinging [...] is like having your cake and eating it too. [Ibid.] 19: My wife and I got into swinging [...] after fifteen years of marriage.
‘Swinging Etiquette’ Honey Rivers’ World of Erotica [Internet] CLOSED SWINGING: This involves participating in swinging (again having sex) in a separate room from your primary partner. The male will be with the female of the other couple in one room and the female with the other male in a different room or at a different time (but still together – not swinging ‘separately’) [...] OPEN SWINGING: Swinging (having sex) in the same room (possibly in the same bed) with your primary partner and another couple. The male will be with the female of the other couple and the female will be with the male of the other couple.
[UK]L. Theroux Call of the Weird (2006) 134: Like some other prostitutes [...] she’d got into the business via swinging.

In phrases

soft swing(ing) (n.)

a partner-swapping party where the only intercourse is performed by couples who arrived together; non-penetrative sex, however, is enjoyed at random; thus soft swinger n.

www.swingingheaven.co.uk [Internet] Soft Swing means no penetration with anyone but your own partner. Often people wanting a soft swing will be quite specific about their own particular boundries. Sometimes it’s just same-room ‘voyeur’ fun, or sometimes it can mean going as far as touching others, or perhaps masturbation and oral with others.
‘Swinging Etiquette’ Honey Rivers’ World of Erotica [Internet] Soft swinging involves teasing and foreplay with another couple prior to returning to your own partner for actual intercourse. Soft swingers prefer to keep actual intercourse between themselves and their primary partner, rather than sharing it with other people.
[US](con. 1973) C. Stella Johnny Porno 208: The Happy Couples lounge had advertised soft and hard swing nights, the former being introductory for newcomers [...] and the latter for more experienced couples.