Agreement
An explicit, negotiated understanding between partners about how the relationship will operate — distinguished from rules in modern polyamory writing by being mutual rather than imposed.
Agreement is the term modern polyamory writing tends to use in place of rules. The distinction matters. A rule is something one partner imposes on another's behaviour; an agreement is something partners arrive at together about how they want to operate.
Healthy agreements share several features. They are arrived at through actual conversation, not unilateral declaration. They cover specific situations rather than blanket categories. They are revisable when circumstances change. They tend to focus on protocol (how things are handled when they come up) rather than on prevention (banning behaviours). They are honoured by both partners because both partners want what the agreement is producing, not because one partner is enforcing it on the other.
Examples of typical polyamorous agreements: how disclosure works (what gets shared, when, in what form); how safer-sex decisions are made and communicated; how time is allocated across partners; how new partners are introduced to the existing structure; how conflicts get raised and worked through. None of these are about preventing partners from having outside connections; they are about how the connections coexist with the existing structure.
Agreements drift. The agreement that worked for the first year often doesn't fit the third year. The community-tested practice is to revisit agreements explicitly on some periodic basis (every six months, or after major life events), rather than letting them silently calcify into resentment.