I have always identified as "nonmonogamous", and that's it. To me that describes what it needs to-- that I am not monogamous by nature-- and leaves the rest open to whatever it ends up being.
For me it just means that if someone comes along that I develop feelings for and things seem to move towards having some type of relationship--whether that be a more involved relationship, or a friends with benefits relationship-- I have the opportunity to go there without dumping my already established relationship. That's about it for me.
Mind you, I haven't done that much because I don't meet people that I would like to be more than friends with much, and most of the time when I do they are not in a position to be more than friends with me. So if you look at the pattern of my relationship for the past eleven years, it would seem mono (at least on my side). It's more that the option is available, whether or not I use it.
I do think that there is a divide in ALL communities when it comes to people thinking X means "blah blah blah" and anybody that claims to be X without being "blah blah blah" is wrong. Mostly, I think it has to do with the tendency of many (most) people to overlook that their OPINIONS are just that-- opinions, and the tendency to think if someone else's opinion is different, then they are wrong. This goes for everything and anything you can have an opinion on.