The definition of "dark pattern" has been evolving. Today I think it means "UI design I don't like", or at least that's how everyone's been using it.
Recently saw someone accuse PayPal of using dark patterns when they clicked the submit payment button and the payment went through (they wanted one more interstitial).
Usually dark patterns are viewed as design patterns that implicitly coerce or deceive the user. As opposed to a banner that explicitly, verbally tells the user to do something.