Only time I will even remotely accept Non-binary as a thing is in the show/manga Knights of Sidonia where people can legitimately change gender depending on their partner. (One of the Genetic engineering developments for deep space exploration so you wouldn't have to worry about the only males or females being left to continue the species)

Izana (Pictured) is non-binary, neither female or male until finds partner, then decides. Y'know like frogs and **** .

Non-binary literally just means neither one or the other. Effectively anything outside 0 and 1, in this case male or female. Effectively these idiots invent new genders, now gender disphoria is a legitimate thing, but to the degree these people take it, it's just purely non-functional.

If you want an unbiased definition, it's the minority of individuals who don't think that the gender binary construct can effectively define what their gender is.Some feel they are both genders, some feel they are neither, some feel they are something entirely different.

If I may be brutally honest though, I can wrap my head around the concept of Gender Disphoria to a point, but there's a point where this needs to stop and we've clearly passed it. If these people want to function in real life, they need to get a clue.

Nonbinary Gender:
Look at me I'm ******* special, give me attention that my parents didn't give.