An ex-girlfriend of mine was the master of the word "whatever." Most people can make "whatever" mean, "I have no preference," or "I'm not interested in this conversation."

Only a master can, with a particular enunciation and facial expression, use "whatever" to convey, "Pick the right choice, idiot;" "Please do not wear that;" and, fatefully, "I'm sorry, but I don't think we are the right people for each other and I wish you good luck in future endeavors."

We don't get to use facial expressions or tones in our bidding. However, the meaning of a word, just like the meaning of a bid, can change based on the circumstance.

What does a 2NT rebid by opener mean? It depends.

In an uncontested auction where responder makes a 1 level response, a 2NT rebid by opener shows 18-19 points and a balanced hand. If responder bid a major, it denies four-card support for responder’s suit (but could have four cards in the other major).

Here are some examples of hands that would bid 2NT after the auction starts:

A)

AJ2
K32
KQJ2
A98

B)

KJ32
A9
AQ98
KQ3

C)

K2
A32
KQJ43
KQ7

The 2NT rebid with 18-19 points makes sense in the context of the auction. Partner has shown very little (some teachers say 6+ points, but most experts respond with an ace or any reason). That means we don’t need much “extra” from partner to belong in a game. Most of the time, partner will get us to at least 3NT.

That said, bidding 2NT gives partner room to use New Minor Forcing or Check Back Stayman or any other convention to find a major fit and explore for a potential slam.

Bidding only 2NT also allows partner to stop if they hate their response. Many players mistakenly bid 3NT with 19 points, which can wreak havoc on an auction. Trust partner to continue over 2NT with a good 6-count. If partner has QJxx xx QJx xxxx, 3NT might not be such a good contract, but with AJ10x xx J1098 xxx, partner will bid 3NT.

A jump to 3NT after opening on the 1 flevel is a “trick showing bid”. It typically says “I want to play 3NT because I have a long suit and a little bit outside". An example would be: x Ax Q10x AKQxxxx - a hand that can take a lot of tricks in notrump, as long as the opponents don't take their tricks first. Notice that this is NOT a balanced hand, even though we bid notrump.

You probably knew most of that, but what if we throw a wrinkle in:

Is this 2NT rebid by opener 18-19? No. Here, we are forced to the 2 level by partner. Employing 2/1, 2NT simply shows a balanced hand. Most of the time, we have 12-14 balanced.

What about this one:

Is 2NT 18-19?

Yes (and a club stopper). This time partner has still shown the same lousy 6 (or fewer) points. In order to make 2NT, we’ll need to have better than 12-14 points. With a balanced 12-14 you simply pass and allow partner to bid again later (they are guaranteed to get a chance).

What about this auction:

Since partner is forcing you at the 2 level, a 2NT rebid shows a club stopper, and a minimum hand. Partner's bid here only shows 10+ points. If you bid 2NT, partner may pass. That means that if you have 18-19 you’d better do something more exciting than a 2NT call. You could jump to 3NT or cuebid.

One last auction to chew on :

Would this be the way to show 18-19?

No! This time, partner has shown 0 points. None! Bidding 2NT puts you at risk. Well, what do you bid with 18-19? 1NT in this auction promises 18-19. Why? With 12-14 balanced, you would pass (or balance with a takeout double). You don’t want to play even 1NT with 18 opposite 0, but at least you’ll have a chance. If you try 2NT, you might see penalty doubles in your future.

The context is key. When partner shows 10+, rebidding 2NT does not promise anything extra. When partner shows a responsive hand on the 1 level, rebidding 2NT is 18-19 points whether or not it’s a jump. When partner shows 0, you typically won’t jump to 2NT if you can bid 1NT.