Polysexuality, also spelled plysexual or polisexual is the exact same fucking thing as Bisexual. It's also a great example of Bi-erasure.
The romantic equivalent to Bisexual is Biromantic.
The polysexual flag has three stripes, pink is for same-sex/gender attraction,blue is for different sex/gender attraction, and purple is to represent the attraction across the gender spectrum.
Bisexuality is romantic attraction, sexual attraction, or sexual behavior towards males, females, and other sexes/genders. Bisexuals can also be attracted to two or more genders at the same time with or without a preference.