Heteroflexibility is a form of a sexual orientation or situational sexual behavior characterized by minimal homosexual activity in an otherwise primarily heterosexual orientation, which may or may not distinguish it from bisexuality. It has been characterized as "mostly straight".^[1] Although sometimes equated with bi-curiosity to describe a broad continuum of sexual orientation between heterosexuality and bisexuality,^[2] other authors distinguish heteroflexibility as lacking the "wish to experiment with ... sexuality" implied by the bi-curious label.^[3] The corresponding situation in which homosexual activity predominates has also been described, termed homoflexibility.^[4]

As of 2010, most studies of heteroflexibility have focused on young men and women, especially white women in the college environment.^[5] Research suggesting the influence of prenatal androgen exposure on female sexual identity places heteroflexibility on a continuum with bisexuality and lesbianism.^[6] Other studies have focused on social origins for the behavior, such as the shifting media presentation of bisexuality or the "socialization of the male interloper fantasy" in which a man is invited into a lesbian relationship as a third partner.^{[7][8][9][10]}

Unlike "bisexual until graduation" and similar pejoratives, heteroflexibility is typically considered to have a positive connotation, and is often a self-applied label, although use of the term as a pop-culture slur has been attested.^[11]

Openly gay sexologist and author Joe Kort has described homoflexible men as "a gay man who has come out and embraced his identity fully as a gay man and chooses to have sex with a woman." Kort stated that homoflexible men are rewarded with some degree of heterosexual privilege by straight people:

In the 60's and 70's, sexual identity was defined with much more fluidity than during the 80's and 90's when clear, defined sexual orientations were considered acceptable. Scientists have noticed a return of flexible sexualities, notably in the case of what it means to be heterosexual.^[13] Social scientists Carillo and Hoffman have seen that men who have occasional sex with other men include the identity of heterosexuality in their behavior. The men in Carillo and Hoffman's study do not identify as bisexual. They see themselves as heterosexual and behave with masculinity while not being inherently attracted to men.^[13] In addition, some men in the study state that occasional sex with men is a result of female unavailability, or perversion. Sexual attraction is a combination of physical and emotional attraction according to the men in Carillo and Hoffman's study. They claim that while they feel romantically, physically, and emotionally attracted to women, their attraction to men is purely sexual lacking any emotional attraction. Furthermore, some of these heteroflexible men do not find other men to be handsome or attractive themselves, but say that they are physically attracted to penises. A heteroflexible management strategy for these men is to interpret their sexual practices with women to be more important than their sexual encounters with men. Some of the men and women who experience same sex encounters while identifying as heterosexual do so to avoid the negative social consequences that come with identifying as a member of the LGBT community.^[13]

National surveys in the U.S. and Canada show that 3 to 4 percent of male teenagers, when given the choice to select a term that best describes their sexual feelings, desires, and behaviors, opt for "mostly" or "predominantly" heterosexual. With "100% heterosexual" being the largest assumed identity, "mostly-heterosexual" was the first runner up in self-identification.^[14] Of the 160 men interviewed for a study in 2008 and 2009, nearly one in eight reported same-sex attractions, fantasies, and crushes. The majority had these feelings since high school; a few others developed them more recently. And in a national sample of young men whose average age was 22, the "mostly straight" proportion increased when they completed the same survey six years later. An even higher percentage of post-high-school young-adult men in the U.S. and in a handful of other countries (including New Zealand and Norway) make the same choice.^[15]

An analytical review article looking at the experiences and meanings of same-sex sexual encounters among men and women who identify as heterosexual found that a large portion of same sex encounters occur among those who identify as heterosexual. The prevalence of same-sex sexuality among heterosexually identifying men and women is not universal. 13.6% of women and 4.6% of men reported attraction to members of the same sex, while 12.6% of women and 2.8% of men have at some point had a same-sex sexual encounter. Findings from the National Survey of Family Growth data from 2011-2015 revealed another insight into how much same sex attraction and behavior can be accounted for by heterosexually identifying people. They found that 61.9% of women and 59% of men with currently reported same-sex attractions, identified as heterosexual. Similarly, 65.2% of women and 43.4% of men who have engaged in same-sex sexual encounters identify as heterosexual.^[13]