of, relating to, or characterised by being any gender that does not fit into the male-female gender binary; an umbrella term.
For example, a non-binary person may have some gender between male and female, have multiple genders, no gender, a culturally-specific gender (e.g., two-spirit).
Non-binary people may or may not also identify as transgender.
Although non-binary is commonly used as an umbrella term, just because someone identifies as a term under the umbrella, does not necessarily imply that they identify as non-binary as well. For example, someone may be agender, but not identify with the term "non-binary".