Compulsory heterosexuality is a term coined by
Adrienne Rich to describe the idea that society forces people, particularly women, to be heterosexual rather than allowing a free choice of
sexual relationships. For example,
lower pay for women in most countries may be considered a compelling mechanism, since it pressures women to marry men in order to achieve
financial stability. In the article which introduced the term, "
Compulsory Heterosexuality and Lesbian Existence" (1980), Rich argued that this oppresses not just lesbians, but all women, and that
feminists should not attempt to
distance themselves from
lesbian causes.
Assuming that someone is heterosexual or considering heterosexuality to be the "default setting" is usually called heterosexism; it's just one (albeit oft-cited) of the many social and economic factors making up compulsory heterosexuality.