This popular convention is used when the OPENER rebids 1NT or 2NT. Responder bids the new minor as an When a suit is bid but says nothing about the holding in that suit artificial way to ask about (or "check back" on) the majors.

Example Auctions: In each of these auctions, responder's second bid is new minor forcing. The responder is asking the opener about the majors (typically looking for 3-card support).
1.

OPENER	RESPONDER
1	1
1NT	2

2.

Opener	Responder
1	1
1NT	2

3.

Opener	Responder
1	1
2NT	3

New minor is used only by the responder and always as his second bid of the auction. It promises at least invitational (10-11) strength (after a 1NT rebid) and some doubt about what the final contract should be. In most cases, the responder will have 5 cards in his major and be trying to decide if the hand should be played in his suit or in notrump.

Examples for Responder to match the auctions above:

1. 1-1-1NT-2:
   K Q 10
   A Q J 7 3
   Q 3 2
   3 2
   
2. 1-1-1NT-2:
   A Q 10 8 5
   K J 7 5
   K 2
   5 4
   
3. 1-1-2NT-3:
   
   K J 8 5 4
   5
   Q 7 6
   7 6 5 2
   

In each hand above, the responder is hoping the opener can show 3-card support for his major. When the new minor is bid, the opener must ALERT. If the opponents ask, he can explain: "My partner's bid is When a suit is bid but says nothing about the holding in that suit artificial and forcing for one round. He is asking me about my majors." The opener now should show 3-card support if he has it (with 4-card support he would have raised on the previous round). If the opener doesn't have 3-card support, his next obligation is to show 4-cards in the other major. If he has neither of the above, he makes the cheapest bid he can (over clubs he bids diamonds; over diamonds he bids notrump).

Meanings for Opener:

Opener	Responder
1	1
1NT	2
??

2=3-card heart support
2=4 spades, but not 3-card heart support (unlikely since no 1 bid)
2=None of the above.

Opener	Responder
1	1
2NT	3
??

3=No major
3= 3-card heart support
3=4 spades (not 3 hearts)

*Note: If you play this convention, make sure partner is playing it the same way as you. I suggest you play it as written here, but some people play that on Opener's 3rd bid he bids his cheapest major (up-the-line). (In other words, he might show 4 hearts before showing 3-card spade support.)

Examples for Opener:

1. K Q 2
   J 4 3 2
   A Q 2
   Q 7 6

OPENER	RESPONDER
1	1
1NT	2
??

Bid 2 (unless you are playing that you show hearts first with 4 hearts and 3 spades)

2. A Q 3
K J
K Q 10 5 2
K 4 3

OPENER	RESPONDER
1	1
2NT	3
??

Bid 3 (Denying 3 and denying 4)

3.

AQ
AJ5
A10432
K103

Bid 3

Follow-ups (Responder's 3rd Bid):

Opener	Responder
1	1
1NT	2
2	??

A bid of 3NT is "Choice of games," promising 5 cards in his major.
A bid of 4 of the major is to play.
A re-raise is invitational.

Examples:

KJ954
AJ3
K54
J2

On the auction above, bid 3NT to offer opener a choice between 3NT and 4 (he will know you have 5 spades to have gone this route).

KJ954
3
KQ4
KJ72

On the auction above, bid 4 to play in the 5-3 fit (this hand is too shapely to offer opener a choice between 3NT and 4).

KJ954
3
KQ4
Q872

On the auction above, bid 3 to invite game in the 5-3 fit.

Note: "New Minor" should NOT be on in competition (of any kind). Decide if you wish to use it by a Passed Hand (No strong feelings--just make sure to discuss).

"New minor" can be used after 1-1-1NT (with 2 being the aritificial bid).

You might consider Larry's recorded webinar on New Minor Checkback found HERE.