I am all for more language to describe love and the varieties of innovative ways to do relationships and chosen family. "Ethical non-monogamy" is a great term that encompasses all the ways that you can consciously, with agreement and consent from all involved, explore love and sex with multiple people.
So here's a simple list to categorize the many flavors of ethical non-monogamy:
1) Polyamory This word literally means loving many. Polyamorous people are usually interested in living together and growing deeper bonds. A household can be any configuration. Two women + one man, etc. A "quad" or foursome, and groups larger in size with various agreements. How can you not love this word and idea?
2) Swinging The general idea is that you engage in sex play, but aren't looking to develop a long-term relationship. Some swingers are in a committed relationship and go to swing parties together to find a single or a couple to play with.
3) Polyfidelity is used to describe a closed set of relationships, whether a triad, a quad or more. You are sexually exclusive with the people in the relationship "system."
4) Primary Relationships and Secondary Relationships Some people configure their relationships with a central (primary) relationship and one that is more "on the side" (secondary). Others find these distinctions insulting, making the secondary person feel, well, secondary.
5) Sexually Monogamous Polyamory Hang in there, did I just confuse you? There are folks who have a beloved that they are married to or live with, and also have someone else that they are in love with and/or have a deep erotic attraction to but do not have sex with. Everyone involved is fully on board with the arrangement. You could say these practitioners are sexually monogamous but emotionally polyamorous.
6) Open Marriage This is somewhat of an umbrella term that encompasses many different arrangements and agreements. Typically, it means that there is some flexibility in the marriage to explore sexual encounters and/or relationships with others. But again, the setup can look vastly different from one open marriage to the next. Some open marriages lean toward poly with deeper ties to lovers, others lean toward swinging with more fleeting sexual encounters.
7) Everything in Between Just when you thought this was going to be simple! People are unique in building their communities and constructing all kinds of setups: friends with benefits, married and dating, polyfidelity with some swinging occasionally, and so on. Someone recently wrote me: "We opened our marriage and now we are doing something equidistant from poly to swinging." The varieties are endless.
I offer this list to share all the creativity out there. It's meant to give some names to the different ways we can make intimate connections with others -- because, why not broaden the possibilities for who we choose to love? -- and how we can set it up to creatively meet all the needs of those involved. But, please remember people don't fit into neat little categories. Labels are ultimately for cans of soup. So be authentic, and do it your way!