“Sex” refers to the biological and physiological characteristics that define men and women.

“Gender” refers to the socially constructed roles, behaviours, activities, and attributes that a given society considers appropriate for men and women.

To put it another way: “Male” and “female” are sex categories, while “masculine” and “feminine” are gender categories.

Aspects of sex will not vary substantially between different human societies, while aspects of gender may vary greatly.