Earlier quoted context omitted.
When I talk about fluidity of gender, or gender distinct from sex, I start with well accepted terms. Consider: you would probably agree with me that a butch tomboy and a valley girl fashionista are both women. But they represent different extremes on what we, socially, agree femininity is. We might say the butch woman is less feminine than the valley girl. Likewise, we'd typically say Clint Eastwood is more manly tha…
"gender" as a term on its own is used very confusedly by a lot of people, but there's a simple definition that makes things clear: "gender == sex". The trick is that "gender" disambiguates that you mean "sex as it relates to a social context" instead of "sex as it relates to a biological context". Where this all gets cleared up is that you should use more specific terms such as "Gender norms", "gender presentation",…
There's a wide variety of genders in the rest of the world as well. While this is a newer concept in American and Western cultures, there are non male, non female genders dating back to mesopotamia.