There is no difference between bisexual and pansexual. Bisexual was coined to mean people attracted to both sexes. Then, decades later in the 80s, bisexual was split up into pansexual, a lack of gender preference, and polysexual, attracted to some but not all genders, to further elaborate on the bisexual spectrum. Polysexual never really caught on, but pansexual had a previous meaning created by none other than Freud himself, meaning sexuality free of boundaries, including incest and beastiality. Some people used pansexual to mean a voracious and nondiscriminating sexual appetite. Almost all bisexuals just called themselves bisexual, so it was the weirdos who called themselves pansexual and used to mock bisexuals as being close minded. Then this softened over the years and was used by people really into being kinky and queer. Then it was used to mean someone specifically into trans people, sometimes trying to be considerate and inclusive, sometimes just being a chaser. And then in the last decade, people started redefining what bisexuality is to mean preferences. Pansexual is still used by people who identify too much with gender. Bisexual is still the standard used by bisexuals and the LGBT community. But that's how everything evolved.