CoinJoin - Definition from the Hotspot Shield Encyclopedia

CoinJoin is a method of anonymization for Bitcoins transactions that was created by Gregory Maxwell.

The process works on the idea that making a dual payment with another user at the same time will make it virtually impossible to trace a payment back to the person who initiated it. A single party payment can easily be traced back to the one person involved, whereas a joint payment using two or more users will mean that the direct of the money movement will remain unknown. A downside to the CoinJoin transaction method is that users must negotiate a transaction and be trusted by a third party server to achieve this - Storing data and making transactions on a third party server leaves room for attacks and the transaction being compromised.