Those who are on the non-binary spectrum of genders exist outside of the gender binary of male/female. It can also refer to the gender identity by the same name; this form of non-binary is generally the same, except that it is the identity of an individual rather than a group. Another option is no gender, as non-binary means "absence of binary" .
The spectrum ranges from the non-binary identity to demi-male or demi-female to genderfluid, to any other gender that isn't strictly male or female.
Official Non-binary Flag