any relationship arrangement that is not sexually or romantically exclusive. on its own the word says nothing about honesty: when it is done with everyone's knowledge and agreement it is ethical or consensual non-monogamy; without that agreement it is simply cheating. the word that matters is the one in front of it.
It is worth separating the plain word from the ethical practice, because they are often blurred. Non-monogamy only describes a fact: more than one connection. What makes a given arrangement healthy or harmful is not the plurality but the consent. A secret affair and a fully negotiated polycule are both, technically, non-monogamy; only one of them is ethical non-monogamy.
want to talk about Non-Monogamy with people who live it?
definition contributed by Tessakin