Bridge

A 2NT response to a 1-of-a-major opening replaces the natural invitational 2NT (which would be wasted since we have a fit). It promises 13+ HCP and 4+ trumps, forcing to game, and asks opener to describe their hand further: shortness in a side suit (3♣/3♦/3♥/3♠ = singleton or void in that suit), 3NT = 15-17 balanced, 4 of the major = minimum with no shortness. Responder uses this information to evaluate slam.