Semi-forcing Notrump
As a variation, some partnerships choose to play their 1NT response as semi-forcing. The rebids and subsequent auctions are the same as with the forcing notrump, except that the opener is allowed to pass with a 5-3-3-2 minimum and no interest in game opposite a limit raise (including 3-card support for opener's major).
This changes follow-up auctions in that opener is assumed to either have 4 or more cards in any new suit bid, or some extra values when holding only 3 cards in a newly bid minor.
Read more about this topic: Forcing Notrump