I really, truly hate when people conflate the terms GNC and ‘Nonbinary’ (or just don’t know what GNC means at all), so here you go:
GNC (Gender Non-Conforming): Not identifying with/actively practicing the societal gender roles assigned to your sex
Ex. Males who wear makeup and skirts (still men), females who don’t shave and cut their hair short (still women).
‘Nonbinary’: Identifying out of the “gender binary”
I.E. Trying to claim that they are neither men or women.
They. Do. Not. Mean. The. Same. Thing.