Dorothy: It's in an X-File.
Dales: An "X-File?"
Dorothy: Yes. Unsolved cases. I file them under "X."
Dales: Why don't you file them under "U" for "unsolved"?
Dorothy: That's what I did until I ran out of room. Plenty of room in the "X's."
Dales: Who decides when a case gets an "X"?
Dorothy: The Director's office. It's, uh--It's kind of a dead end. No one's supposed to see them, but it makes for interesting reading.
Dales: Do you know what an...X-File is?
Mulder: It's uh--Yeah, it's an unsolved case.
Dales: No, it's a case that's been designated..."unsolved."