According to a trans glossary I found it means "assigned female at birth", so a doctor looking at your junk and seeing that you are anatomically female, writes down "female" in the birth recrods. Fine, I can follow that, but let's get to "demigirl"... Demigirl:  A demigirl (also called a demiwoman or a demifemale person) is a gender identity describing someone who partially, but not wholly, identifies as a woman, girl or otherwise feminine, whatever their assigned gender at birth. They may or may not identify as another gender in addition to feeling partially a girl or woman.  But wait, it gets more snowflaky. From a "safe space for demigenders" on tumblr:  Demienby: someone who identities partially as enby; “enby” is a noun and a name for a gender which acts just like “girl” and “boy” do; not all non-binary individuals consider themselves “enby” Demifluid: someone whose gender is partially fluid with the other part(s) being static; an example could be: one part of their gender is “woman” while the part that fluctuates is  ”man” and “genderqueer”. Demiflux: someone whose gender is partially fluid with the other part(s) being static; this differs from “demifluid” as “-flux” indicates that one of the genders is neutral; an example could be: one part of their gender is “genderqueer” while the part that fluctuates is “agender” and “woman”. I hope this clears things up a bit.  Savage   Now that is fucking special if you ask me.