Basically, being attracted to not just two sexes like bisexual implies. They're attracted to ALL genders. This means the pansexual person is attracted to, or can be attracted to, males, females, intersexes, pangenders, androgynes, agenders, genderqueers, bigenders and many more.
1: Are you bisexual?
2: No, I'm pansexual. I like all genders, not just two like "bi"sexual implies. Because pan means all.