In terms of body trends that become popular on social media, the internet doesn’t exactly have a great track record. While there are many positive and inspirational fitspo posts to help you get and stay motivated, on the other side of the coin there are strange and dangerous trends (like the thigh gap test and A4 waist challenge) that make you shake your head and wonder what’s wrong with the world.

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Is an Ab Crack a Real Thing?The latest body trend that has the interwebs talking (and stalking newsfeeds) is called the “Ab Crack.” This newly coined phrase (that sounds a lot like another crack on your body), is meant to identify the vertical line that separates the abdominal muscles in super well-defined abs. “The linea alba (which means white line) is made mostly of collagen connective tissue,” says FitFusion celebrity trainer Andrea Orbeck.“It’s formed by the fusion of the abdominal muscles’ aponeurosis (pearly white fibrous tissue), and it separates the left and right rectus ab muscles.”

You don’t have to be Jen Selter or Emily Ratajkowski to have an Ab Crack. You just have to be fit enough (in other words, ripped) and lean enough to see the dividing line. “A so-called Ab Crack in the central abdomen is no different than the horizontal lines that define a six pack,” says New York plastic surgeon Daniel Maman, MD. “The fitter you are, the bigger your rectus muscles will be and the more chiseled your abdomen will appear.”

According to Orbeck, having an Ab Crack doesn’t mean you’re overly fit. The images being used to illustrate an Ab Crack show that it has more to do with having a lower percentage of body fat than developing larger muscles. “Genetically, some people may have more pronounced grooves than others, but you’ll notice in the photos of these models, who are very lean, they don’t actually have very developed abs,” says Orbeck. “They just have the groove, which means they are leaner than they are stronger in their core.”

Is It Actually a Medical Condition?The separation of your left and right rectus muscles is also a common medical condition called diasteses recti. “Diastese recti is a physical separation of the rectus muscles at the midline, or more specifically a spreading of the linea alba,” says Dr. Maman. “Nearly 100 percent of women who have been pregnant will have some degree of diastases recti. The stretched out ab muscles and the midline connection never restore themselves to a point of fusion.”

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Although this condition is more common in women post-pregnancy, it can happen to anyone who experiences weight gain or overworks their abdominal muscles with rigorous exercise. “With diasteses recti, there is permanent damage to the collagen structures of the abdominal wall and a significant loss of tissue elasticity occurs. A major component of a tummy tuck procedure is to repair this diastases recti by sewing the left and right abdominal muscles back together at the midline, which helps recreate the vertical groove that is being referred to as an Ab Crack,” says Dr. Maman.

As with all social media–fueled fitness trends, looks can be deceiving. What appears to be a deep vertical line in an Instagram photo may be a lot less pronounced in real life. “The bottom line is that we all technically have this vertical split, you just have to be at a low enough body fat percentage to see it,” says Orbeck. “Social media images, photoshop and filters alike, if you don’t actually do the time in the gym and eat properly, your hashtag will read #niceabstoobadyoucantseethem.”