The word "Bad" is 21st century slang term. The word "Bad" is formally used to tell about something that is not okay or even awful. But in our use of "Bad" it is used to tell about an attractive person.
WORD:BAD DEFINITION:AN ATTRACTIVE BOY OR GIRL Used in a sentence: "Dang you see that girl over there? She's bad, I'm gonna go get her SnapChat"