Conventions in depth
A jump to 2NT over an opponent’s opening that shows at least five cards in each of the two lowest unbid suits.
The player holds at least five cards in each of the two lowest unbid suits and about 8 or more points (nearer 10 when vulnerable). The bid can be made directly over the opening or in the balancing seat.
A natural 2NT overcall would need a balanced hand and a stopper, a rare holding not worth a special bid. The strength range is wide, from a hand bidding to obstruct or sacrifice up to one with game interest; the five-five shape is what the bid promises.
Because the two suits are already known, advancer’s task is to choose the better of them and bid it at the appropriate level: higher with a fit and values, lowest just to compete.
Unusual 2NT and the Michaels Cue-Bid are the two two-suited overcalls. Michaels cue-bids the opponents’ suit to show the majors, or a major and a minor. Unusual 2NT jumps to notrump to show the two lowest suits, most often both minors. Between them, almost any five-five two-suiter can be shown in a single bid.
