Veto is a rule that hands one partner the power to shut down another partner's outside relationship — often with no reason required.
Veto lives in hierarchical non-monogamy, where an established couple treats itself as headquarters and everyone else as a branch office. The deal is blunt: if your other relationship makes me uncomfortable, I can order you to end it, and you comply. Some versions are "absolute" — no reason needed, ever. Softer ones treat a veto as an emergency brake: a signal that something is badly wrong, not a day-to-day remote control.
Here's the catch the word hides. A veto gets exercised on someone who never sat at the table. The third person — the "secondary" — gets dumped by a partner they trusted because someone they may have never met made a call about their life. Educators keep landing on the same image: when one partner can command the other to break up, you've stopped being partners and turned into parent and teenager. That dynamic breeds exactly what you'd expect — resentment, sneaking around, and relationships that suffocate instead of ending on their own terms.
For a long stretch, veto was the default poly advice: protect the primary, keep the rules, don't let the newcomer get too close. That's shifting. The distinction people now draw is between descriptive hierarchy — the real weight of a shared mortgage, kids, a decade of history — and prescriptive hierarchy: rules invented to keep a third person structurally beneath you. Veto is the loudest prescriptive rule of them all, and increasingly the community's answer is the same: manage your own discomfort, talk to your partner, and don't outsource a breakup to a clause.