It's when teens send nude or inappropriate pictures to friends and those things end up on the internet for the world to see.
"Essentially sexting is just a new way for teenagers to flirt," said Eyal Yechezkell, CEO of NextWeb Media and Predicto.
But sending racy photos via text also means teens are flirting with danger.
"The problem with that is it doesn't just go to that person, but then that person sends it to another person and then a rumor mill starts and it causes a lot of problems and heartaches for a lot of students when all that gets out," said Jeri McBeth, a personal social counselor at Topeka High School.
"I think they need to think about what they're doing and think about the consequences," McBeth said.
Some who get caught sexting can face trouble with the law.
"The authorities are arresting some of these teenagers for exchanging nude photos," Yechezkell said.
In fact, some teens are facing charges related to sexting, including child pornography charges.
The whole mess is something Yechezkell and McBeth agree parents could help prevent.
"Parents really have to be involved though and set some rules upfront with their children - rules about using their phones and rules about using the internet, too," McBeth said.
"What parents need to do is actually evaluate before they give a cell phone to their children," Yechezkell said. "The texting part is so personal to the point where you tend to forget someone on the other side could potentially share the information."
You can have your cellular service provider shut off the text messaging feature on your child's plan, but experts say even just talking with them about the consequences may get them to think twice before hitting the send button.