The gender binary, also referred to as gender binarism (sometimes shortened to just binarism), is the classification of sex and gender into two distinct, opposite and disconnected forms of masculine and feminine. It is one general type of a gender system. As one of the core principles of genderism, it can describe a social boundary that discourages people from crossing or mixing gender roles, or from identifying with three or more forms of gender expression altogether. In this binary model, "sex", "gender" and "sexuality" are assumed by default to align; for example, a biological male would be assumed masculine in appearance, character traits and behavior, including a heterosexual attraction to the opposite sex. Classification within this gender binary does not encompass individuals who are born with non-binary reproductive organs and may exclude those who identify as lesbian, gay, bisexual, transgender, transsexual, genderqueer or third gender.