Polyfidelity is non-monogamy with the door shut: three or more people committed to each other, equal in standing, and closed to anyone outside the group.
Take polyamory — many loving relationships at once — and then lock the group. That's polyfidelity. Nobody dates out, nobody sleeps out; the circle is the circle. Think of it as monogamy's math done with more than two people: the exclusivity is fully intact, it's just pointed at a group instead of a couple. A triad, a quad, a whole household — the headcount varies, the closed door doesn't.
The word that trips people up is "equal." In classic polyfidelity there's no primary and no side piece: everyone counts the same, no ranking of who matters most. That's the pitch and also the hard part, because keeping several people on genuinely level footing takes more honesty and more admin than most couples manage with two. Adding a person isn't a solo decision; it's a group call. Someone leaving reshapes everyone. The closed structure that makes it feel safe is the same one that makes it slow to change.
Historically the closed part doubled as a sexual-health strategy — a bonded group testing and staying within itself, long before PrEP made that math looser. And that framing came straight from where the word was born: Kerista, a utopian commune in San Francisco that ran on "polyfidelity" from the seventies to the nineties, rotational sleeping schedule and all, to keep things even. They coined "compersion" in the same kitchen. So if the term sounds a little idealistic, that's not an accident — it was built by people trying to solve loneliness and jealousy with a spreadsheet and a lot of conviction.