McKendrick

This is a convention used to deal with a weak hand with long diamonds after opener's 1NT. A 2S response shows either 11+ point hand, or a weak hand with a long minor. The reponses are:
3C with a maximum. Responder passes with clubs, converts to 3D with weak diamonds, or makes some other bid.
2NT otherwise. Responder bids 3C with clubs, 3D with weak diamonds, or makes some other bid.