Someone (usually white male) who goes and gets laid by dirty, filthy Polynesian woman (the scum of the earth) who are all fat, smelly, hairy and look like men.

An attractive female or male that enjoys playing sexually with people that are married but non-monogamous or polyamorous

A fun plaything.

If a particular Poly Pocket happens to be a young, attractive bisexual female who dates entire couples, she would also be a unicorn