[Serious] Non-binary

[Rev. Rye]

Semantics.

Here's the definition of Gender according to the Oxford English Definition, specifically 3b:

 b. Psychology and Sociology (originally U.S.). The state of being male or female as expressed by social or cultural distinctions and differences, rather than biological ones; the collective attributes or traits associated with a particular sex, or determined as a result of one's sex. Also: a (male or female) group characterized in this way.

1945   Amer. Jrnl. Psychol. 58 228   In the grade-school years, too, gender (which is the socialized obverse of sex) is a fixed line of demarkation, the qualifying terms being ‘feminine’ and ‘masculine’.
1950   Amer. Jrnl. Psychol. 63 312   It [sc. Margaret Mead's Male and Female] informs the reader upon ‘gender’ as well as upon ‘sex’, upon masculine and feminine rôles as well as upon male and female and their reproductive functions.
1968   Life 21 June 89   When the separation of fashions according to gender began to vanish, retailers discovered a bonanza.
1978   D. Pearce in Urban & Social Change Rev. 11 i–ii. 35/1   The major implication for policy of both the feminization of poverty and the..labor-force participation of welfare mothers is that gender cannot be ignored.
1981   Heresies 3 67/3   Our ideology and practice of sex roles construct..two mutually exclusive categories, that is, genders.
2007   New Yorker 6 Aug. 13/2   There's no breaking news here—identity and gender have been on the contemporary-art docket for years.

The distinction between gender and sex is really nothing new, as the quotes section shows. That said, it looks like the OED has yet to fully codify how some people have seen fit to take these notions of gender and go beyond the binary of male and female into their definition. The OED is being updated constantly, although it can take a bloody long time for them to codify terms. You remember how they added a new definition of "literally" that blatantly contradicted the original meaning in 2013? That meaning's been in use since before America declared independence from Britain.