A transcorder implant is piece of Dominion technology that documents the memories and experiences of a Vorta with the purpose of transferring them to a subsequent clone in the event of the Vorta individual's death. The implants continuously upload information to the Dominion subspace network.
In 2375, Julian Bashir discovered a transcorder implant while autopsying the sixth Weyoun clone. When Miles O'Brien attempted to study the device it self-destructed. When Weyoun Eight was killed by Elim Garak at the end of the Dominion War, Odo retrieved the transcorder implant and later used it to give the ninth Weyoun the memories of the previous Weyoun clones. Other Vorta, such as Vannis, also had transcorder implants. (DS9 - Worlds of Star Trek: Deep Space Nine novel: The Dominion: Olympus Descending)