What does nonbinary mean? Very simply put, it means not two groups. So a nonbinary framework of gender is one that recognises there’s not just two genders (e.g. only girls and boys). That’s the easy bit.
When someone is talking about their gender and they say they are nonbinary it can mean different things. What you know is that they are not only a girl, nor are they only a boy. They might be a girl and a boy. They might be neither a girl or a boy. Nonbinary is an umbrella term to describe all the genders other than “girl” and “boy” – according to some there are 58 different genders and according to others there’s as many genders as people! It’s also a gender itself sitting under this umbrella.
You might see it written as “nonbinary” or “non-binary”. As far as I know, one is not more correct than the other. The nonbinary colours, as represented on the nonbinary flag, are yellow, white, purple, and black.