Some useful terms:
- A closed sexual relationship involving more than two people. Heinlein’s line-marriage concept is one form of polyfidelity.
- Primaries & secondaries
- Some polyamorous folks distinguish between one (or more) primary relationship(s) and one (or more) secondary relationship(s). The distinction generally refers to the level of commitment in each relationship rather than issues of time or affection.
- Body-fluid monogamy.
- The practice of sharing body fluids with only one other person (and thus using safer-sex practices with other people). When the concept is extended to more than two people, it is generally referred to as pooling risks. Thus, all primaries in a polyamorous relationship might pool their risks, but practice safer-sex with secondaries and/or casual lovers.
- A term used in some relationships made up of three people. Generally polyfidelitous, and m-m-f or f-f-m.