The thigh gap refers to the space between a person's thighs when they're standing straight up and their feet and knees are together.
It's commonly seen in runway models and movie stars, but now it's also becoming a dangerous obsession for many teenage girls.
"I've seen a lot of posts on the internet and different things about the thigh gap like 'would you rather have a thigh gap or cake?' And stuff like that," said Taylor Hawes of North Carolina when asked if she knew of the thigh gap trend.
Nutritionist Larissa Gedney says girls are taking extreme dieting measures to try and get the gap, and that these measures can lead to permanent body damage.
"It can affect other parts of your body such as giving you brittle nails and dry hair, flaky skin. So you may be targeting one area of your body, but your entire body will be affected," Gedney said.
Gedney also said what many girls don't realize is that the chances of getting the perfect thigh gap are slim.
"Its not very attainable, one, because your body is not built to look like that. It's not natural. And you have to go to extreme measures that end up being very unhealthy to get your body to look like that," Gedney said.
Gedney blames today's image-driven society for dangerous trends like the thigh gap, and said the pressure to be skinny is hard to escape.
"The way women are portrayed in the media, in magazines and on TV usually shows someone that's very thin and it can give especially young girls a false perception of reality," Gedney said.
Gedney said the best thing parents can do is talk to their children about healthy body images and to look out for warning signs that your child may have an eating disorder.
You can learn more about the warning signs here.