Devised by expert Alvin Landy, this convention stipulates that a 2C overcall of 1NT shows at least
4-4 in the majors and 12+ points. All other overcalls of 1NT are natural, and Landy applies in both direct and balancing seat. 

The responses to 2C are:

Pass: Long, strong clubs with no interest in the majors
2D: Long, strong diamonds with no interest in the majors
2H/2S: Signoff, although overcall is allowed to bid again. 
2NT: 12+ points, one-round force. Partner is asked to bid a five-card major if he has one, or 3C/3D
to show the respective minor-suit stopper with 4-4 in the majors. 
3H/3S: Invitational