For anyone who writes about social codes, Manhattan is a rich environment, teeming with information. Sometimes, all you have to do is listen. By the time I stood at a very loud party in a lavishly decorated uptown venue a few months ago, I had heard a lot. I had written about the private lives and cultural practices of very wealthy New Yorkers and now, for every person who ran the other way upon seeing me, another one wanted to tell me things. Often, perhaps because I had supposedly lifted a veil on a secretive, private world, people talked to me about the ultimate secretive, private topic: sex.

I often heard about affairs. While the names and players sometimes surprised me, the facts did not: what anthropologists call “extra pair copulations” are common. In her meta-analysis of 133 cultures worldwide, anthropologist Meredith Small found not a single one without infidelity.

I heard about high-earning men having affairs “because they could,” and about wives with money of their own having affairs “because they weren’t afraid to.” This was no surprise. The anthropological data show that she who brings home the bacon (or mongongo nuts or small animals caught in nets) has increased clout and autonomy. Indeed, sociologists tell us it’s no coincidence that, as women have entered the U.S. workforce over the last decades—34 percent of women in the U.S. worked in 1950, versus nearly 58 percent by 2012—they have also begun to close the “infidelity gap,” cheating at close to the same rates as men, according to Bloomberg News.

The affairs people told me about made sense, seen through the prisms of anthropology and sociology. And then, something surprised me.

At the party that night, the music blared. Some women and I were chatting about sex. A 30-something fashion plate and mother leaned toward me and whispered, “What about the [inaudible]?”

It sounded like she said, “pushy whistlers.”

Sorry?

“The pussy whisperers!” she repeated. “The trainers who have affairs with their clients during summer in the Hamptons!”

It sounded like a variation on the pool boy cliché: a hot working guy, the beautiful wife of a wealthy man who works in the city during the week, the kids at sleep-away camp…But I hadn’t heard the term—which implied a particular skill set, and a special knowledge about what women want—before. “Well,” I said, “if these men are attractive and attentive to their female clients…”

“The pussy whisperers,” she interrupted, “are women!”

***

“Saturday Night Lesbian,” “Bicurious” and “MARBLE—Married but Lesbian” are all vernacular terms that point to a popular awareness that female lust can be shape-shifting, flexible. Lots of people in my world knew the famous story of the gorgeous mommy who had left her successful husband for her charismatic female spin instructor. The couple was out and proud, spinning side by side. But “pussy whisperers”? The descriptor hinted at a practice that would seem off the map for the women I had written about, to say the least.

Or not.

Thanks to the inroads paved by LGBTQ activists and feminists in recent decades, as well as the work of mostly female sex researchers, there seems to be a new openness in discussing sex and gender not as we think it should be or want it to be, but as it is actually experienced. This may in part explain why what we might call “female flexuality” is having a zeitgeist-y moment. From “it” girl Cara Delevingne’s involvements with both women and men to Kristin Stewart’s recent declaration that me not defining [myself as gay or straight] right now…is what I’m all about”; from engaged-to-a-guy Piper’s not-so-straight affairs on Orange is the New Black and even Gloria Vanderbilt’s recent revelation, while promoting her new book, of a girl/girl dalliance at Miss Porter’s back in the day; to Skirt Club, a women-only roving party in London, Miami and Manhattan, where the female owner who is married to a man says most of those who come to “play” with other women are in relationships with men, too—“heteroflexible” women are entering the mainstream. Articles in women’s magazines (“A Closer Look at Women Who’ve Left Their Husbands for Other Women,” for instance) and headlines that alternately trumpet and vociferously deny that studies show women’s preferences are “mostly gay or bi,” give it all a news-y spin.

A former trainer whose mostly female clients lived uptown and in the Hamptons recounted that it was not unusual for her married female clients to come on to her.

Sex researchers have also been focused on female flexuality. Based on results of a 10-year longitudinal study of 79 women, University of Utah sex researcher Lisa Diamond coined the term “female sexual fluidity” to describe the malleability of female desire. Dr. Diamond discovered that circumstances—an accepting community, an open-minded female friend, an emotional connection—might contribute to a woman who has spent years or decades feeling and being heterosexual to have sex with a woman. And decide to keep doing so. Or not.

Other research has focused on female desire. Meredith Chivers, associate professor of psychology, at Queen’s University in Canada found that women may have more category-defying tendencies than men (straight women are more likely to be excited by lesbian porn than straight men are by gay male porn, for example), and be turned on by a wider array of images and fantasies.

Dr. Alicia Walker, visiting assistant professor of sociology at Missouri State University, conducted a pilot study of women who are married to men but seek out female partners online for in-person sexual encounters. These women refused titles like “gay” or “bisexual,” identifying themselves instead as motivated by what they described as their “strong” libidos and “freakiness” to search for clandestine sexual encounters with other women. Dr. Walker uses the term “undercover,” as one of her interview subjects did, to describe the desire for women that hums alongside and coexists with their heterosexuality. While we’re rethinking categories, as such behaviors might lead us to do, let’s put to rest the notion that it’s all “just a phase” for younger women who are “gay until graduation”; a recent Glamour survey of 1,015 women between 18 and 44 found 47 percent had been attracted to another woman, and nearly 1 in 3 reported a sexual experience with another woman.

In spite of overall social shifts and trends and statistics, it seemed odd that the hierarchy-and status-conscious married women with children I spent time with—women who live in what can certainly be described as a heteronormative culture—might go against tribal custom and get sexually involved with women—particularly those who might fall into the “help” category. But there were specific circumstances that suggested they might not be an exception to the sex research data. Like women in Hollywood, those I studied live in a body-display culture with unyielding standards. Women must be ultra-fit, beautiful and youthful. Period. Some took two exercise classes daily. And I knew from the way they gushed about their instructors, rushed to sign up for their classes, followed them on social media and confided in them as a previous generation had their hairdressers, that many established close bonds with these “body shamans.”

Whether it’s a supermodel, a Netflix series, a moniker like “pussy whisperer” to describe a relationship, or a study by a sex researcher, our culture is currently experimenting with the notion that the course of female sexuality cannot necessarily be predicted, defined, or confined. And that we might need new vocabulary—in addition to straight, bi and gay—to describe it.

“Yes, I know about the female [exercise] instructors who seduce women away from their husbands,” a beautiful blonde socialite told me with an “everybody knows that” wave of her hand. A man who socialized and worked with a group of wealthy, married Hamptonites told me about two women, each married and avowedly heterosexual, each having a passionate affair with a woman—one with a woman who was her exercise coach. A therapist told me about a married woman who brought the female trainer she had long fancied on a trip to train her—and they ended up in bed. Her client, said the therapist, “believed it ‘didn’t count as cheating.” A master of the universe, I was told, found out his wife was sleeping with her female physical therapist and forgave her, presuming she would end it. She refused; they divorced.

A former trainer whose mostly female clients lived uptown and in the Hamptons recounted that it was not unusual for her married female clients to come on to her. “They’d say, ‘I think about you all the time,’ ” she said over lunch at a Brooklyn restaurant, where her physique (tall and ripped) and classic beauty drew admiring stares. She recalled that, before she moved West and traded training for a 9-5 job, she sometimes used that erotic connection to motivate clients. Trainers want people to succeed and feel motivated, she explained, and “if being attracted to us helps, O.K.” She also conceded that in her trainer days she had mixed business with pleasure (she used an expression that was far saltier) and knew of other female trainers who slept with their married, assumed straight female clients, too.

“It’s sort of the new workplace affair, but with a different ‘workplace,’ and genders switched around,” observed a Manhattan workout aficionada who was aware of the whispers about pussy whisperers. She noted that she had heard the term “straight whisperer” to describe the phenomenon, as in, able to whisper a straight woman into bed.

“Isn’t it just that when you’re a woman who has it all, having a female lover is an experience you might allow yourself to have?” a woman who summers in Sagaponack mused, surprised that anyone would be surprised.

***

I’m not at all surprised to hear about assumed heterosexual women having affairs with their female trainers,” said Dr. Walker, who teaches a popular “sociology of sexuality” class at Missouri State University, by phone. “The more honest dialogue we have about women’s sexual practices, the more we find these types of experiences among women who don’t claim a label other than heterosexual.” While there are no hard and fast numbers or large-scale statistics on how many avowedly heterosexual women pursue liaisons with other women, they may be higher than those suggested by the Glamour study. That’s because, as psychologists, sex researchers and sociologists tell us, it is notoriously difficult to coax interview subjects to disclose the full extent of their stigmatized or taboo behaviors. This is especially the case with women, who face particular biases—slut shaming, sexism and double standards among them—when it comes to fully and frankly disclosing their sexuality. And still, many experts echo the observations of Yale lecturer of psychiatry Binnie Klein, who told O Magazine: “It’s clear that a change in sexual orientation is imaginable to more people than ever before, and there’s more opportunity—and acceptance—to cross over the line.”

Ms. Klein added that six of her married female patients had become involved with women over the last several years. Rachel Blakeman, a psychoanalyst in private practice on the Upper East Side, concurred. In her clinical experience, women may be more likely to cross the line in their minds than in reality. “Female sexual desire is more complex and fluid than male sexual desire,” she said. “Some women who identify as heterosexual and exclusively partner with men, have erotic desires that extend to women. The reasons each woman chooses to fulfill her sexual desires for another woman at a particular time or under certain circumstances, as opposed to resisting…or feeling it less powerfully at other times, is unique to each woman—but what these women all share is a sexual fluidity.” Perhaps this is why Joanne Fleisher, LCSW offers a “Workshop for Married Women Attracted to Women” on May 22 in Philadelphia, and Match.com created a category called “Women Who Leave John for Jane.”

The anthropological data suggest that female flexuality is not just a Western thing. In Lesotho, a small country surrounded by South Africa, women whose husbands are away for extended periods may take a motsoalle, or special female friend. And in Suriname, working-class Creole women who are called mati have relationships with both men and women, not infrequently living with their female lovers and children. Many !Kung adolescent girls in Namibia experiment with other girls sexually, with adults viewing it as “inevitable and normal,” according to anthropologist Melvin Konner of Emory University.

Whether it’s a supermodel, a Netflix series, a moniker like “pussy whisperer” to describe a relationship, or a study by a sex researcher, our culture is currently experimenting with the notion that the course of female sexuality cannot necessarily be predicted, defined, or confined. And that we might need new vocabulary—in addition to straight, bi and gay—to describe it. Dr. Diamond’s work suggests that in particular, we have yet to wrap our minds around how much female sexuality has to do with context.

Decades ago, social scientists had already coined a term for the tendency of women in places like women’s prisons and all-girls’ schools to have sex with one another (men have sex with men in prison, of course, but “heterosexual women are significantly more likely to have consensual sex with female partners in prison compared to heterosexual men in prison,” noted Dr. Dylan Selterman, a lecturer at the University of Maryland’s psychology department). They attributed such “situational lesbianism” that occurred when there were few or no men around to a psychosocial dynamic they rather unfortunately dubbed “the harem effect.” The exoticism of the term smacks of an anxious assertion: “It can’t happen here.” An alternative descriptor—such as “segresexuality”—may more accurately suggest that, wherever women spend a great deal of time with other women in the relative absence of men, female flexuality increases the likelihood that those who are assumedly heterosexual may become sexually involved with a woman nonetheless.

***

Which brings us back to the pussy whisperers. How, I wondered, could women who did not have their own money and income act on their flexuality? Wouldn’t their financial dependency, and their dependent offspring, along with their traditionally gender-scripted marriages and comparatively conservative culture, hold them hostage to some sort of heterosexual normativity?

Perhaps. But not necessarily. Because along with economics and autonomy, experts tell us, it turns out that opportunity also plays a significant role in whether someone has an affair. Women flooding the workforce in recent decades found not just earning power and independence, but increased exposure to potential sexual partners.

“Opportunity” looks a little different in the Hamptons, among a group of largely non-working women who are out East for the whole summer, often attending sex-segregated luncheons and fundraisers and trunk shows, socializing in weekday evenings with mostly other women, and working assiduously on their bodies in the presence and with the guidance of female trainers, some of them gay, while their husbands work in the city. These women have autonomy of a different sort, and opportunity aplenty.

“Contextual variables make it more or less likely for women to act on their female flexuality, and the Hamptons is just one place worldwide where a perfect storm of factors can aid its expression,” believes biological anthropologist Natalia Reagan. Her viral Huffington Post Science piece “Hooray for Gay Animals” addressed the spectrum of sexual behavior in a variety of animal species—including our own.

All this may be a summer cocktail potent enough to render some avowedly heterosexual women, as the data suggest is not uncommon, something else as well: “segresexuals” who are “gay until Labor Day.”

Wednesday Martin, Ph.D. is the author of the No. 1 New York Times best-seller Primates of Park Avenue, now available for pre-order in paperback. She has contributed to The New York Times and The Atlantic, and taught cultural studies at Yale and The New School for Social Research.

Some identifying details have been changed to protect the anonymity of sources.