The gender binary (also known as gender binarism) is the classification of gender into two distinct forms of masculine and feminine, whether by social system, cultural belief, or both simultaneously. Most cultures use a gender binary, having two genders (boys/men and girls/women).
In this binary model, gender and sexuality may be assumed by default to align with one's sex assigned at birth. This may include certain expectations of how one dresses themselves, one's behavior, sexual orientation, names or pronouns, which restroom one uses, and other qualities. For example, when a male is born, gender binarism may assume that the male will be masculine in appearance, have masculine character traits and behaviors, as well as having a heterosexual attraction to females. These expectations may reinforce negative attitudes, biases, and discrimination towards people who display expressions of gender variance or nonconformity or those whose gender identity is incongruent with their birth sex.