Heterosexism is a system of attitudes, bias, and discrimination in favor of heterosexuality and heterosexual relationships. According to Elizabeth Cramer, it can include the belief that all people are or should be heterosexual and that heterosexual relationships are the only norm and therefore superior.
Although heterosexism is defined in the online editions of the American Heritage Dictionary of the English Language and the Merriam-Webster Collegiate Dictionary as anti-gay discrimination or prejudice "by heterosexual people" and "by heterosexuals", respectively, people of any sexual orientation can hold such attitudes and bias, and can form a part of internalised hatred of one's sexual orientation.