An SOS redouble named after its Swedish inventors, which asks partner to choose another suit when the opponents have doubled.
The principle is that at low level you should be content to play in any making doubled contract and so would not want to redouble in a natural sense and allow the opponents to escape into some other contract.
On this auction, East’s Kock-Werner redouble asks West to bid again. East is going to have a singleton or void in clubs and at least five cards in each major.