So, you know how when you grow up, you learn about having sex and how it's something adults do when they love each other and want to make babies?
Well, some people believe that if they have sex before they get married, it's not right because it's supposed to be something special that they only share with their husband or wife. And if they do have sex before marriage, they might feel bad about it and wish they didn't do it.
So, a "born-again virgin" is someone who has had sex before but wants to start over like they've never had sex. It's kind of like when you erase a picture and start fresh.
They might say that they're a born-again virgin because they want to forget about the old stuff and make better choices in the future. And that's okay, because everyone makes mistakes and it's important to learn from them and do what you feel is right.