Are you a boy or a girl?

Eily Mixson, 18, answers neither.

"I have a firm sense that I'm definitely not a girl," says Mixson, a recent high school graduate. "Having been questioned, 'Am I boy then?' I can pretty definitively say, 'No, I'm pretty sure that's not the case.'"

Z Murphy, 17, wakes up some days and binds her breasts, puts on a man's suit and adds a fake, flaccid penis in her pants. Other days, she wears a dress and make-up.

Soren Barnett, 18, gets unsettled when people use the words boy or girl. So Soren will escape to the bedroom, blast orchestra music and study French to drown out the swirling thoughts.

All three identify as nonbinary, or a gender other than strictly male or female. And all three might change how they identify from day to day, or even moment to moment.

More commonly, they might be called "genderqueer," "agender" or "gender fluid." Whereas transgender people typically identify differently than their assigned gender at birth, nonbinary people often are not concrete.

That also makes identifying them tricky. Some prefer gender neutral pronouns such as "they, them" or "ze, zir." Others are okay with "he, she."

To experts in the lesbian, gay, bisexual, trans and queer community, nonbinary people are the next frontier in human gender identification -- so new that some struggle to fully understand what's happening.

"This is challenging our ideas of biological sex and issues of gender," says Michael LaSala, an associate professor at Rutgers University who specializes in LGBTQ research. "Everything (for so long has been) divided by pink and blue. We don't quite know what to do as a society with the idea that not everybody falls into those categories."

The emergence of this group comes at an interesting time. As the nation wrestles over transgender bathroom rights and overall acceptance of the group, how will the debate over nonbinary people play out? How might it impact the nation's long-held notions of gender identity? And will it complicate strides being made for gay and transgender rights because the nonbinary movement can be so confounding?

"We've become comfortable with our idea that, 'This person's a man, this person's a woman,'" LaSala says. "When you start talking about people who desire to straddle those differences, it starts to blow people's minds."

Now, those long-held gender notions are being challenged in potentially groundbreaking ways.

"I do feel that I have a gender," Eily says. "I just have not found a word to articulate it yet."

Soren Barnett, 18, gets dressed at home in Montgomery. (Andre Malok | NJ Advance Media for NJ.com)

'I GO BY ALL PRONOUNS'

Z Murphy tries describing her gender on a recent Saturday during a stop at a deli in Highland Park. But her girlfriend at the time, Kristen Medina, keeps playfully interrupting.

"I am ..." Z begins.

"A trainwreck," Kristen cuts in, grinning.

The table erupts in laughter. Then Rob DiGioia, a friend sharing lunch, tries to steer the conversation back on track.

"Stop it!" he says. "Let him talk."

The pronoun "him" doesn't bother Z, who was assigned female at birth but now identifies as gender fluid. That means she floats between genders depending on how she feels that morning, that day or that moment.

"I go by all pronouns," Z says. "He, she, they, them, your majesty."

On this afternoon, Z, who just finished her junior year at Highland Park High, has her hair blown out in a Diana Ross afro. A silver hoop hangs from the bottom of her nose, and she's wearing a frayed Bob Marley tank top and black tights. She seems to be presenting female, even though it's not necessarily her intention.

"I don't really know how to explain when I feel like doing so-and-so; it just happens," Z says. "I'll wake up and I'll want to wear a dress. I'll wake up and I'll want to wear a men's jersey. Like, there aren't really any rules and I'm comfortable with that."

Her journey has carved a jagged path.

As a child, Z loved dresses and asked to be called "princess." But then she would take the role of husband when playing house. By age 10, she says she stopped wearing dresses, instead favoring oversized jeans, T-shirts and hoodies. Soon, she was telling her mom she felt masculine. Z then started binding and packing and asking her mom to call her "child" or "kid," not "daughter."

At one point, Z thought maybe she was a transgender boy.

"Personally, I was having a lot of difficulty with the idea that she might be a trans boy," says Z's mom, Pandora Scooter.

"But my main message to her was that no matter where she landed on the gender spectrum, I loved her no matter what."

When she was 14, Z says she went to Buck's Rock Performing and Creative Arts Camp in Connecticut and met two biological females who wore their hair short with shorts one day, then dresses and makeup the next.

"I asked them, 'Why are you wearing dresses?'" Z remembers. "And they said, 'Because we're gender fluid and we can wear whatever we want.'"

Something clicked.

Z came home and began presenting both masculine and feminine, and she now identifies sexually as "pansexual," which means she's attracted to people of any sex or gender. The labels may sound confusing, but friends say they mean nothing when they're hanging out.

"I'm dating a person," says Kristen, Z's girlfriend at the time. "I say 'girlfriend' to simplify it for others more than anything. But when I think of Z, I don't think, 'Oh, my girlfriend' and I don't think, 'Oh, my boyfriend.' I just think, 'Z.'"

Z Murphy, 17, prepares for her girlfriend's prom. (Andre Malok | NJ Advance Media for NJ.com)

'IS THERE SUCH THING AS THAT?'

The gender binary begins at birth when a baby is immediately assigned as male or female. Often, it happens even earlier with an ultrasound and then gender reveal parties.

But the emergence of nonbinary and similarly identifying people has gained enough momentum in the past several years to challenge those norms, says Corrine O'Hara, a long-time LGBTQ youth advocate in New Jersey.

About 13 percent of transgender and gender nonconforming people surveyed in 2012 said they didn't identify as either male/man or female/woman, according to the National LGBTQ Task Force and the National Center for Transgender Equality. And 20 percent of the 6,434 participants said they identified part time as one gender, part time as another.

Similarly, a 2013 national survey of LGBTQ students ages 13 to 21 found 11 percent identify as genderqueer, while 4 percent selected "another gender," such as agender or gender fluid. The study, conducted by GLSEN, one of the nation's leading LGBTQ organizations, was the first by the group to include genderqueer as an option.

More people are identifying under the nonbinary umbrella because of the growing acceptance and understanding of LGBTQ issues, says Jill Marcellus, director of communications for the Transgender Law Center in Oakland, Calif. The sheer fame of Olympic champion and reality television star Caitlyn Jenner, who came out as a trans woman in 2015, has helped educate.

"We're in a place where more people are feeling able to come out and talk about how their identities don't fit in the typical boxes that folks associate with gender," Marcellus says. "We've seen an increase in people feeling they're able to live as their authentic selves."

That poses a challenge for everyone from governments and private employers to schools and hospitals. For years, transgender people have been pushing for rights to more easily change their genders on licenses and birth certificates and have equal bathroom access. But what about people who don't want to identify as either male or female? Or people who want to identify as both?

"It's new -- that's why people are confused and it's not discussed as normal compared to transgender," says Jackie Baras, co-facilitator of a transgender family support group at Robert Wood Johnson University Hospital in Somerset. "Even us, even in the community, we're kind of like, 'Really? Is there such thing as that?'"

The bathroom issue is popping up in school districts across New Jersey, and nonbinary people are presenting their own unique challenges since some may be comfortable using both the "girls" or "boys" room. Sue Henderson, a guidance counselor at Ocean Township High, said her school offers bathrooms in the nurses office and another single stall as gender neutral options for transgender or nonbinary students.

Meanwhile, Eily most often uses the "girls" bathroom at school or in public because that's the gender others often perceive her to be, and Z also uses the "girls" room most often mainly out of convenience. Soren tries to use single stall bathrooms at school that are considered more gender neutral, and said using the "girls" room can be particularly difficult.

"Using the women's rooms is pretty awful because those who don't know me give me strange looks and think they're in the wrong bathroom," Soren says. "(It) just makes me uncomfortable and again aware of gender."

Z Murphy,17, identifies as nonbinary, a gender other than strictly male or female. (Andre Malok | NJ Advance Media for NJ.com)

'A MESS IN MY HEAD'

Soren, who prefers gender neutral pronouns such as "they, them," tends to be analytical, so exploring gender identity can be mentally exhausting.

"The not knowing is sometimes very uncomfortable," Soren says. "It's just such a mess in my head."

Assigned female at birth and given the name "Sarah," Soren does a double take when someone refers to Soren and other students together as "girls." Catching a glimpse of breasts before stepping into the shower is confusing "because I just forget they're there," Soren says.

Soren then will consider identifying as male, "but my brain immediately goes to the arch-type, the macho male, and I'm like, 'No, I'm not that.'"

Soren recently graduated as an A student at Montgomery High in Somerset County and calls homework a "coping mechanism." It's complicated enough being a teenager, and wrestling with gender only adds to Soren's angst.

"I don't really know what it means to be male or female," says Soren, who will attend Skidmore College in Saratoga Springs, N.Y. this fall.

Eily can relate.

Also an A student, Eily came across the notion that gender is not binary while visiting an online forum for young novel writers six years ago.

The threads were divided into posts for boys and girls, and Eily questioned why there needed to be a distinction. That's when another poster wrote that there are people who don't identify as either boys or girls.

"That was a defining moment because I knew then," says Eily, who was assigned female at birth. "I was like, 'That's what I am.' Everything made sense."

Eily, who says ze wants to study neuroscience or "something to do with thinking and the brain" next year at Williams College in Massachusetts, often analyzes the idea of gender. When it comes to feeling masculine or feminine, Eily says ze doesn't feel like either.

Teens and experts say the nonbinary movement is not a fad, and that it could be one step in a journey toward ultimately identifying as one gender or the other. Others will go their entire lives under the nonbinary umbrella.

"I still don't have an exact word for what I feel," Eily says. "I've sort of used the umbrella term mostly because I know I fit into that umbrella, but it's hard to pinpoint where.

Nonbinary: A gender-fluid generation speaks out 19 Gallery: Nonbinary: A gender-fluid generation speaks out

Matthew Stanmyre may be reached at mstanmyre@njadvancemedia.com. Follow him on Twitter @MattStanmyre. Find NJ.com on Facebook.