It's 'polyam' not 'poly'. Which is short for polyamorous, which means more than one partner.
'Open relationship' is having a partner but you have permission to sleep with other people.
Polygamy is marriage to more than one person, and is illegal in this country but works for many people in other countries, such as some fundamentalist Christians and some Asian religions.
Pansexual (I'm this one) Is merely a sexual orientation. I beer towards men, my partner is male. But I've previously dated women, pre-op transsexuals, post op transsexuals, transvestites, people who like me identify as non binary.
Some of us fall for the person inside, not the package.
I admit, the polyam people I've known have been rather loud in a vegan way about it. I just nod and smile. I don't care what anyone is as long as they're happy.