Heteronormativity is an expressed used to describe or identify a social norm relating to standardized heterosexual behavior, whereby this standard is considered to be the only socially valid form of behavior and anyone who does not follow this social and cultural posture is placed at a disadvantage in relation to the rest of society. This concept is the basis of discriminatory and prejudiced arguments against LGBT, principally those relating to the formation of families and public expression.

Source: LGBT Communication Manual, Brazilian Gay, Lesbian, Bisexual, Transvestite and Transsexual Association and UNAIDS.