Kinktionary
More like guidelines and a lot less like definitions.
Non-Binary
A person whose gender identity falls outside the male-female (or man-woman) binary.
Non-binary can be any mix of male and female, any xenogender or neogender (identifying one's gender as something alien, for example), agender (no gender), or anything else that isn't "just male" or "just female."
It is up to individuals if they identify with the label of non-binary, and how they identify with it, whether it be as a vague umbrella or as their own specific gender identity on its own.
Non-binary can be shortened to "enby" or "NB." Note that some people object to the latter abbreviation because it's historically been used to mean "non Black" and may be perceived as appropriation.