Having more than one sexual partner either concurrently or serially.
The term "promiscuity" has fallen out of favor with social scientists, epidemiologists, and others who seek to rationalize human behavior, who use instead the seemingly neutral "multipartnering."
Multipartnering is also employed by apologists for the "sexual revolution," who object to the term "sexual promiscuity" because they believe it implies a negative, usually faith-based, moral judgement of sexual behavior.
(See, for example, Douglas Feldman's defense of "polypartnering" in the Alliance policy paper "Multipartnered Pansexualism or Heroic Love.")
Nevertheless, multipartnering, or sexual promiscuity, is what creates epidemics of sexually transmitted diseases (STDs), and the two groups in Western societies who have the highest rates of multipartnering also have the highest prevalence of sexually transmitted diseases: prostitutes, referred to by social scientists as "female sex workers," or FSWs; and gay / bisexual men, referred to by social scientists as MSM -- men who have sex with men.
And of course it's the combination of the ubiquity of anal penetration and the very high rates of promiscuity among gay-identified men which led to and sustains the MSM AIDS epidemic.
Among gay-identified men in particular, there are several well-established forms of promiscuity, including group sex, open relationships (in which couples say they're "committed, but play" either together or separately), and "friends with benefits," men with whom men get together regularly for casual sex without an emotional committment.
And these forms of promiscuity can occur simultaneously.
A man who's in an open relationship may go to a sex club where he has group sex -- including possibly being penetrated anally by as many as twenty men; then, on that same evening, meet a "friend with benefits," with whom he has sex privately; and then return home to his partner, with whom he also has sex.
This scenario is not far-fetched (see, for example, the discussion of barebacking in Multipartnered Pansexualism or Heroic Love), and is what is responsible for the very high prevalence of HIV and other anally-vectored diseases among gay-identified men.
The ideology of promiscuity / multipartnering is deeply entrenched in mainstream gay male culture.
Here, for example, is a profile, found on a popular on-line gay male dating site, of a man who says he's a 43-year-old psychotherapist in a long-term, "open relationship" in a large southern city:
Screen name: "obscenewish"
Self-description: "Just an average, down-to-earth, normal guy in pursuit of your rectum."
Sexual interests: "One-on-One, Three-Way, Groups/Parties/Orgies, Leather/Fetish scenes, Friends with benefits, Couple seeking sexual partners"
Sexual Fetishes: "BDSM [bondage, discipline, sado-masochism], Leather"
In his online diary, he denigrates frottage and indeed any sex which does not culminate in his penetrating another man, and adds,
"I think something is sacrificed - romantic idealism, perhaps - when you open your relationship to outside sexual play but eventually sex becomes the last reason most people stay in a relationship more than five years or so."
For more online profiles of sexually promiscuous gay men, see Multipartnered Pansexualism or Heroic Love.
For a discussion of the entrenched nature of promiscuity among gay-identified men, see Do Gay Men Have to be Promiscuous?
For a discussion of the benefits of Fidelity, see Why Be Faithful?
See also Pansexualism, Fidelity, and Heroic Love.