I've been meaning to ask for quite a while now: What exactly is "flag" supposed to indicate?

I assume it's something more specific than "dislike". I take it to mean something along the lines of, "I think this is (sneaky) spam", or "This does not fit on a technology news site, even tangentially.". Or, perhaps something broader like, "I can't describe what the problem is, but this submission/comment should be reviewed by a moderator."

It's just never been particularly clear what the intention of it is.