Gender, a term used in feminist, self-described "queer" and various other ideologies, means the social dimension of a person's physical sex. Gender includes society's customs and expectations about the behaviour and roles of the various sexes, but also someone's sex identity - what sex they feel they are.
The Twine universe includes several cultures with gender roles that aren't like Earth's (Instar, for example) and several worlds with more than two biological sexes (the Fuzzworld), or biological sexes that are different to Earth's male and female.