A system of responses to a 1NT opener. 2♣️ shows a weak take-out type of hand with length in any suit. It demands 2♦️, which responder can pass or convert to 2❤️ or 2♠️. 2♦️ over 1NT is the Stayman enquiry (2NT denying a four-card major), while 2❤️ and 2♠️ are forcing with a five-card suit.

A jump to three of a major is a slam invitation.