In 1957, Alvin Roth in his partnership with Tobias Stone appropriated the abandoned term negative double to denote a conventional double by responder over an overcall. The bid was also briefly known as Sputnik, because it was as new as the satellite of that name that the Soviet Union had recently launched. In many places in Western Europe, it is still referred to as the Sputnik double.
Negative doubles have become popular because they solve this difficult -- and common -- bidding problem:
S - 762
H - KQ75
D - 94
C - QJ93
Partner opens 1D and your right-hand opponent (RHO) overcalls 1S.
The overcall has taken away your 1H response, so you have no way to accurately describe your strength and distribution.
You can't bid 1NT (which promises a spade stopper) and you can't bid a new suit at the 2-level (which promises 10+ pts.).
The solution is the negative double. To use this convention, you and partner agree that if you open the bidding and the opponent makes a direct suit overcall, a double by responder is NOT for penalty. Instead, it shows:
• Responding values (6+ pts.) AND
• 4 card length in at least one of the unbid suits -- usually the unbid major suit. (Some pairs agree that if the two unbid suits are majors -- for example, after 1C by partner, 1D by RHO -- a negative double promises 4 cards in both suits.
In the problem above, you would double to show the values for a response and a 4 card heart suit.
This tells partner that you would have responded 1H if the opponent had passed. If opener also has 4 hearts, he'll "raise" your response by bidding hearts himself. If not, he can choose another descriptive bid.
Here are some other examples of how you can use negative doubles:
S - A973
H - AJ
D - 92
C - KJ1062
If partner opens 1D and RHO overcalls 1H, make a negative double.
Even though you have enough strength for a 2-level freebid, a 2C bid here will make it difficult to find a possible 4-4 spade fit. Use the double to show your 4 card spade suit, then decide which game to bid over partner's response.
If partner doesn't "raise" your spades, you'll bid 3NT. (After the 1H overcall bid 1S only if you have FIVE spades).
S - K1063
H - 762
D - K72
C - AJ7
If partner opens 1D and RHO overcalls 2C, make a negative double to show at least one 4 card major. If partner bids 2H, you can bid 2NT -- this shows an invitational-to-game hand with a club stopper, but without four hearts. Since you started with the negative double instead of 2NT, partner will also know that you have a 4 card spade suit.