A variation on Stayman with standard replies by opener but which allows responder to use Stayman on a balanced hand not containing a four- card major.
If a 2NT response to 1NT is conventional, responder has to find some other way to invite game in no-trumps, one solution being to start with 2♣.
Using non-promissory Stayman, after opener rebids 2♥, responder rebids 2♠ if holding four spades; 2NT instead would deny four spades.