What is the Feminist definition of gender?

Feminism tends to define gender as a social construction that is separate from a person's biological sex. Sex is determined by physical sex characteristics, and though in the western world it is usually thought of as a binary (male:female) many cultures recognize the existence of 3 or more sexes. Feminist write Anne Fausto-Sterling suggests that there are 5 sexes in her piece "The Five Sexes: Why Male and Female are Not Enough."

Gender is a social concept that encompasses the gender put on them by society as well as their own gender identity. Gender and sex do not always match. For instance, someone identified biologically as a man might identify internally as a woman. Many feminist theorists have developed ideas of fluid gender identity, in which a person's gender is not a fixed definition throughout their lifetime.