There are more than two genders. In the same way, monoamory and polyamory can be seen on a spectrum; gender is no different. However, overall polyamorous education, community events, and access has been binary focused. Even when education includes the spectrum of sexuality, it excludes gender beyond the binary. Understanding polyamory and your sexual and romantic attractions will be limited if you see everything through a binary lens. There are terms in non-monogamy that would be more expansive if the binary weren't the focal point - like polyGAMY to be used as a gender-inclusive term for those who practice multiple marriages. The lack of interest in making polyamory less "he/she" further stigmatizes non-binary people looking to partake in the love style. So much so that when non-binary people speak about dating or relationships, people still attempt to categorize them in binary labeled relationships.
Non-Binary
Non-binary (or genderqueer) is an identity outside the binary of man/woman. Non-binary are under the category of transgender because they do not identify with the gender assigned at birth; however, some non-binary people do not consider themselves trans people. Some people may identify with the term "third gender" due to their ethnic background. Be advised - due to colonization and general white washing, abuse, and misuse, the third gender, depending on the culture, could be severely misrepresented by those who do not identify with that specific indigenous background. Androgyny is the possession of both masculine and feminine attributes in a human. For biological s-x, it may be used to reference intersex people and in gender, non-binary people. To be clear, all non-binary people are not androgynous, nor does it mean they have to be. The concept of androgyny being the poster child for non-binary is rooted in white beauty standards, discrediting non-binary bodies that may be of different shapes and colors.
The Pronouns
As a heads up, pronouns aren't just used by the non-binary community. You can find most people's pronouns on their online profiles/bios. Even if someone presents what you think a specific gender looks like, do not assume. If you do not know and cannot ask, the safest bet is using they/them/theirs pronouns until you learn otherwise. People's identification card does not always correlate to their assigned gender either, and many states still do not have non-binary gender identifiers on their ID cards.
Polyamory
When the polyamorous community as a whole is focused on the binary, non-binary people are excluded. Often, non-binary people will endure misgendering to access education, events, and potential partners. This looks like a non-binary person attending a polyamorous event where the ticket prices were based on gender - man and woman. They may constantly remind their partners that they are not in an MFF triad, just a triad. If the terminology was gender-inclusive, they could feel like imposters in spaces where they belong. Reviewing polyamory through a lens beyond the binary will allow us to see how terms, acronyms, and practices are bigger than man and woman. MFF triad could be referenced as a triad. A non-binary person could be polygamous because they have multiple spouses. A gender-inclusive term for dragon or unicorn could be created. Events could support non-binary people by removing gendered ticket prices. Inclusion also looks like education. Some non-binary people have dead names, names given at birth before their transition that do not align with their identity. Non-binary people with dead names may go through extensive (and expensive) processes to remove any record of that name. Deadnaming someone is using the name they do not use anymore to reference them (with or without their presence), which is VERY harmful. In polyamory, this looks like dating a non-binary person and using their dead name with your partners or calling them it instead of the name they chose for themselves.
The Effects of Colonization
Non-binary people have existed before colonization in various cultures across the world. Sometimes non-binary looks like someone who has the intermediate between the binary or someone who is a spiritual leader/entity for that culture. Colonization severely affected the cultural practices of acknowledging gender beyond the binary. Non-binary people were hypersexualized, ostracized, forced to align to a binary gender based upon their genitalia, or worse.