Non-binary is a spectrum of gender identities that are not exclusively masculine or exclusively feminine—identities that are outside the gender binary. Genderqueer is an earlier term with the same meaning, originating from queer zines of the 1980s.
Non-binary people may identify as having two or more genders (being bigender or trigender) having no gender (agender, nongendered, genderless, genderfree or neutrois); moving between genders or having a fluctuating gender identity (genderfluid); being third gender or other-gendered (a category that includes those who do not place a name to their gender).
Gender identity is separate from sexual or romantic orientation, and non-binary people have a variety of sexual orientations, just as transgender and cisgender people do.
A non-binary gender is not associated with a specific gender expression, such as androgyny. Non-binary people as a group have a wide variety of gender expressions, and some may reject gender "identities" altogether.
Examples of identities on the non-binary spectrum are demiboy, non-binary, and demigirl. These are not all of them, but probably some of the most common.