As a basic concept polyamory is the practice of having multiple sexual and/or romantic relationships at the same time with the knowledge and consent of everyone involved. Literally the word means “many loves”. Although, within the polyamory community, and to each individual it may mean many different things. There is a bit of contention about what constitutes being polyamorous.
For some, the emphasis is placed on the “love” part of the literal definition. I have heard people argue that if it is not multiple romantic relationships that it is not polyamory. Some people will say that any configuration of multiple partners should be polyamory. This would include open relationships (more casual encounters), swinging, serious relationships and anything in between.
I tend to be in the second group. For me polyamory and Ethical non-monogamy are synonymous. Monogamy meaning one sexual or romantic partner and no other serious or casual encounters are permitted.
For me, I think that excluding open relationships or swinging from the poly umbrella excludes asexual and aromantic people and I would also not want to tell someone how to define a relationship or experience that they had. It is possible to have some very passionate, even romantic, casual one night relationships. It is equally as possible to have less meaningful, lackluster relationships that go on for years. Every time you connect with someone that could be a relationship to you.
I think that holding polyamory up on a romantic pedestal runs the risk of slut shaming and invalidating the experiences of other people that may be different from you. You can be single and in no relationships at all and still be a polyamorous person if you are open to the idea of multiple partners. I will admit that I have come across some people who are open or swingers that are very closed to the idea of any sort of connection deeper than the physical and I had a hard time with that. However, it is not for me to tell someone else what to put value on.
Having the option to have multiple partners of any kind is what I think the core of polyamory is. If you feel poly, and you define yourself as such then I would say that is what makes you polyamorous.