The Wolff Signoff is an artificial 3 convention used in the following auction:

Opener	Responder
1-of-a-suit	1-of-a-suit
2NT*	3!	* Balanced with 18-19 points

The artificial 3 bid shows a weak hand, generally with at least five cards in responder's original suit. With three-card support, opener bids that suit at the three-level. Without three-card support, opener is required to rebid 3, artificial. All of responder's subsequent calls over 3 are natural signoffs, with the exception of 3NT, which shows 10-12 points and support for opener's original suit. The 3NT rebid, however, is nonforcing.