Polyamory
Definition
Openly having multiple (sexually intimate) relationships.
It can take many forms: swinging, friends with benefits, free love, open relationships, polygyny, polygamy, etc. The primary feature is that all participants openly consent to the non-monogamous arrangement.
Polyamory sees people as shared assets. The fundamental scarcity of individuals is their limited time, attention or focus. Everything else is an artificial scarcitt. You can share posession of these things not ownership of a person.
Similar to contracts for various shared assets, polyamorists develop complex lists of rules that govern the relationship. Its bounds as well as its commitments are consciously arranged. Polyamorist often use scheduling software to arrange time and availability.
Though many polyamorist tend to favor egalitarian arrangements, they sometimes rank partners as primary or secondary and so on.
Discussion
Polyamory's essential difference with monogamy is its sexual non-exclusivity. Monogamous people already have multiple relationships of varying intimacy levels, just not sexual ones.
Polyamory, and other open forms of non-monogamy, are merely a type of relationship preference. Monogamous relationships that are similarly openly consented to, are an equally valid preference. Both are compatible with P2P values.
History and Future
Polyamory and open non-monogamy likely began with humanity. Hunter-gatherer tribes still practice it even today. Polyamory often arises in the enclaves of networked subcultures opposing the dominant soco-culture regime. The Hippies, Feminist, Gay and BDSM communities are a few examples.
The internet and p2p networks allow for more efficient sharing of posessions, including people's romantic attention. As calendar and scheduling type software develop, new forms of sexual and romantic temporal relationality will be created.
Closed Monogamy/Non-monogamy
Closed monogamy and closed non-monogamy (cheating) are types of relationships where one or more of the participants doesn't know and can't change the terms of the relationship.