Triad

The structural distinction between a triad and a vee comes down to which edges of the triangle are romantic. In a triad, all three pairwise connections exist; in a vee, the “hinge” partner is in two relationships and the other two members are metamours rather than partners. Wikipedia's polyamory entry notes that triads can take many shapes, including configurations Isaac Asimov is sometimes credited with naming, and that the three-person unit is one of the most commonly depicted forms in mainstream coverage even though vees are statistically more common in practice.

Triads can be open (members are free to date outside the unit) or closed. A closed triad in which all three members agree to limit their sexual or romantic connections to the unit is usually called polyfidelitous, a term coined alongside compersion at the Kerista Commune in San Francisco. Polyfidelity carries some of the same household and resource-pooling implications as monogamy: shared finances, co-parenting, joint leases, even legal workarounds for the lack of three-party marriage.

The colloquial “throuple” (a portmanteau of three and couple) tends to appear in mainstream media and dating-app copy, while “triad” remains the term of choice inside the polyamorous community itself. Most experienced poly writers caution that triads formed by a pre-existing couple looking for a third tend to fail along the same lines as classic unicorn hunting; triads that work usually grow organically from three already-connected people rather than from a couple's wishlist.