A call that doubles again the value of the trick score, the penalty for undertricks and the bonuses for overtricks of a contract that an opponent has already doubled. It will also lead to an additional bonus (‘for the insult’) of 100 points if the contract makes.
Redoubled contracts are rare because whichever side loses on the deal is likely to record a large loss. At low levels, many redoubles are conventional, either suggesting general strength or, if the opponents have made a penalty double, the desire for a rescue.