Abbreviation for "female-assigned at birth." Applies to any person who was pronounced female at birth based on genitalia. If a person is F.A.A.B. and identifies as a female, she is said to be cisgender. If a person does not identify as female, ze may identify as genderqueer, trans* or any number of other gender identities inside or outside the gender binary.
Sebastian is F.A.A.B., but he came out as male-identified when he was a young adult.