I've been told, many times, that the word "polyamory" is not really necessary, as it's simply a synonym for "open relationship" or "swinging" (or, depending on the person talking to me, "cheating"). This idea seems to assume that there's really only one kind of non-monogamy, which is kind of silly.
A relationship can be non-monogamous without being open; cheating relationships, polyfidelitous relationships, and religious polygyny are all examples. And a relationship can be open without being polyamorous, as for example people who have lots of casual partners but no loving, intimate relationships.
BDSM throws a monkeywrench into the issue because there are so many ways that people involved in BDSM can be non-monogamous. I've seen people who play at play parties with other folks but don't do so outside play parties and don't form relationships; that sort of arrangement overlaps with swinging. I've seen various flavors of polyamorous and polyfi BDSM relationships. I've seen closed-group non-monogamy that isn't quite polyamory and looks more like closed-group swinging, though God knows there's some overlap between closed-group swinging and polyfi; I've known closed group swingers whose groups stay stable for longer than most marriages do. And there's a sliver of non-monogamous BDSM relationships that don't intersect with anything else; "I'll arrange a gang bang for you and you'll LIKE IT," ferinstance.
And then there's con sex, which overlaps with a whole lot of other stuff. But someone could probably write an entire book about con sex.
I started thinking lately about the various ways in which a relationship can be non-monogamous, and the intersections between different sorts of non-monogamy, and after tinkering around with the notion for a while I've come up with this diagram, which has gone through several iterations.
Mouse over the Xes on the map to see a description of that type of relationship. If you like, or if you're on a device like an iPhone where mouseovers aren't possible, you can click here to open a very large version of the Map, with labels.
This map has gone through several revisions. The original version and many previous iterations were posted first on my blog, where they received quite a lot of attention. If you're interested in the evolution of the map, you can see earlier versions here: