CDS stands for "Credit Default Swap." It is a financial derivative instrument used to transfer credit risk between two parties, where one party (the protection buyer) pays a periodic fee to the other party (the protection seller) in exchange for protection against the risk of default of a particular debt instrument or entity.

In other words, a CDS is a type of insurance contract that allows the buyer to protect against the risk of default of a bond or loan, by transferring that risk to another party. If the bond or loan defaults, the protection seller pays the protection buyer a predetermined amount, which is usually the face value of the bond or loan.

CDS can be used by investors to hedge against potential losses due to default, or by speculators to take advantage of changes in credit risk. CDS played a significant role in the 2008 financial crisis, as the default of mortgage-backed securities triggered a wave of CDS payouts and contributed to the collapse of several financial institutions.

"Failed Credit Default Swap." This can refer to a situation where a credit default swap contract fails to perform as intended, typically because the protection seller is unable to fulfill its obligation to pay the protection buyer in the event of a credit event (such as a default).

There are several reasons why a credit default swap contract may fail, including the insolvency of the protection seller, disputes over whether a credit event has occurred, or the inability of the parties to agree on the terms of the contract.

Failed credit default swaps can have significant implications for the parties involved, as well as for the broader financial system. They can lead to legal disputes, losses for investors, and increased uncertainty and volatility in financial markets.

It's worth noting that credit default swaps can be complex financial instruments, and their use has been criticized for contributing to the 2008 financial crisis. Since then, there have been efforts to increase transparency and regulation in the credit default swap market.