an unusual bid

The opponents (E-W) are vulnerable, you (South) are the dealer.

♠ K Q 3  ♥ Q 10 9 6 3  ♦ 8 7 6 5 3  ♣ -- 

You	West	North	East
Pass Pass Pass	Pass 1 ♠ 5 ♣	Pass Pass All Pass	1 ♣ 2 ♣

Bleah, that wasn't any fun. The opponents are cold for 5 ♣, though you didn't know that ahead of time. Let's try again.

♠ K Q 3  ♥ Q 10 9 6 3  ♦ 8 7 6 5 3   ♣ -- 

You	West	North	East
Pass 2 NT	Pass	Pass	1 ♣

A jump overcall to 2NT is "unusual", and conventionally shows at least 5-5 distribution in the agreed suits. This is a standard call, no Alert is required. As originally conceived back in the dark ages of bridge, the Unusual 2NT always showed the minor suits. In modern usage, a few partnerships still use it for the minors but most experts use it to show the lower two unbid suits (here, diamonds and hearts).

I strongly recommend the "lower two unbid" treatment because it comes into play more often. You and partner should discuss this beforehand, reach an agreement, and mark your convention card accordingly. In the absence of an agreement between you and your partner, the unusual notrump shows the old-fashioned minor suits.

If your side is vulnerable, the Unusual 2NT suggests at least an opening hand. Not vulnerable, particularly against vulnerable opponents, 2NT is more often used as a preempt with a much weaker hand. Not vulnerable against vulnerable, you might even risk an unusual 2NT with a 6-4 or 5-4 shape (but be prepared for the occasional disaster!)

After you've shown your distributional hand, partner can evaluate her hand and bid accordingly. Unless you have significant extra values, don't bid again (e.g., don't tell the same story twice).

But what if you really have a natural 2NT hand, with 22-24 points? Buy a lottery ticket, because today is your lucky day! (Oh, and double for takeout then bid whatever seems right.)

The full deal:

South dealer

E-W Vulnerable

	North
	♠ 9 8 2 ♥ K J 5 4 ♦ A 10 9 4   ♣ 10 8
West		East
♠ A J 10 5 4 ♥ 7 2 ♦ K ♣ K 6 4 3 2		♠ 7 6 ♥ A 8 ♦ Q J 2 ♣ A Q J 9 7 5
	South (you)
	♠ K Q 3 ♥ Q 10 9 6 3 ♦  8 7 6 5 3 ♣ --

You	West	North	East
Pass 2 NT	Pass	Pass	1 ♣

Your 2NT call takes up a lot of bidding space and puts pressure on West. Does West dare introduce spades at the three level? Should West raise opener's clubs, knowing there might only be three of them? Partner knows we have a double fit (hearts and diamonds), all her high cards are working, and she shouldn't let the opponents buy the contract short of the six level.

My five minutes are up, but if you have more time... There is a standard expert defense against the Unusual 2NT. It's called "Unusual Versus Unusual".