What ugly men in their mid-20's yell at attractive teenage girls from cars. Infact, it happened to me today.
You can't tell if you should take it as a compliment or not.
Most likely you looked it up on here because of that certain situation.
It's referring to a sexually attractive, but under aged girl. You hear it less in Canada since the age of consent is 14.
Guy in car: "JAILBAIT!!!"
Friends: "I don't know O_o"
You: *looks it up on urbandictionary.com*. OH MY GOD.