Pansexuality is a fairly new identity. It’s first use probably happened no earlier than maybe 2010. It is often confused with bisexuality. Just like the definition of bisexuality routes from the beginning “bi” meaning two, pansexuality routes from “pan” which means all.
A more formal definition of a pansexual is a person who is emotionally, romantically, sexually, affectionately, or relationally attracted to people regardless of their gender identity or biological sex. The use of the term usually signals a repudiation (or rejection) of the concept of binary (two) sexes (a conception sometimes implied by “bisexual”).
Pansexuality is great because it accounts for everyone on the gender identity spectrum, which as we know is a lot of different identities. This rejection of bisexuality is probably a feeling that that identity is two narrow of just two genders, when there are so many. While it is quite new, I think a lot of are identifying pansexual, or pan, especially because sexuality can be so fluid.