bisexuality is actually a topic that many people don't know the true definition of. it means different things to everyone. from what i've gathered from researching the topic, being bi means you're attracted to (trans) males, (trans) females, and (this one is optional) nob-binary/agender people.
being polysexual is sort of like a make-your-own thing. you could like girls and genderfluid people, but not anyone else. it's not the same as being bi, because bi implies the male/female thing.
being pansexual mean you like everyone. you don't consider gender identity a problem at all, and you are open to anything.
this may not be 100% the truth, but after researching the topic a ton, this is what i came up with.
i'm bi, bi the way :)
mods, please let this pass! it's educational and it's not inappropriate.