Never heard of an ab crack before? If you follow Emily RatajkowskiBella Hadid, or Hannah Bronfman on Instagram, you've probably seen it—but there hasn't been a term for the crease that runs down the center of very flat bellies until now. Elle.com dubbed the ab crack "the new six pack." 

Once you know what to look for, you'll notice ab cracks everywhere: They were on display at Coachella (so. many. crop tops!), in the pages of SI's annual Swimsuit issue, and on the runway at the Victoria's Secret Fashion Show last winter. 

Let's be clear: We're all for strong, toned abs, and there's nothing dangerous about having a crease down the middle as long as you're leading a healthy lifestyle. But like the belly button challenge and the thigh-gap craze before it, we're wary of any viral measure of an "ideal" body that encourages women to strive for a specific physical characteristic—especially one that's difficult or even impossible to achieve. 

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"Not everyone is destined to have a washboard stomach or an 'ab crack,' no matter how hard they work out, or how little they eat," says Health's medical editor Roshini Rajapaksa, MD, an assistant professor at the NYU School of Medicine. "Usually the people who achieve them are fitness professionals or models who are paid to look unnaturally goodwho are also probably genetically blessed."

In other words, the ab cracks you see on social media are likely the result of extreme fitness and DNA. There's no lower-body regimen or diet trick that will guarantee you an ab crack. So rather than striving for this particular look, a healthier strategy is to focus on strengthening your entire core (which includes your back and obliques, in addition to your abs) and eating a clean diet with plenty of fresh produce, lean proteins, pulses, and good fats (think salmon, avocados, and nuts). 

The bottom line, according to Dr. Rajapaksa: "Getting an ab crack is probably not a realistic or healthy goal for the average person."