Group sex involves three or more people, but usually isn't centered around an established couple, as a threesome is. Group sex might originate during a night at a swingers' club, or at a sex club. Sometimes people also seek each other out online. There are more and more sites that make this possible, and it often has the advantage of avoiding the complications of jealousy or the risks of unstable couple relationships.
Group sex can also be part of outdoor, dogging (British English) or adult movie theater activities. The underlying pleasure comes from emotional detachment, and the thrill of getting to know strangers in such an intensely stimulating setting. Although group sex has been a source of mass fun since ancient times, it has its modern caveats.
Safer sex is an absolute must in these contexts, and consent should be in constant negotiation through communication between partners, strangers or not.
More on the beauty of group sex here:
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