IMO, gender identity is who you "are", and expression is how you "present" that. HTH ? As for what "gender" is....I myself am a bit hazy on it. In the old days, gender and sex were used interchangeably. Now they aren't. But regardless, I identify as female - which applies to both gender and sex. I once heard that gender is the expression, sex is the identity (which made sense to me). But if we split gender into 2 categories....I have no idea. lol