The Moment

The Moment was something with which, or a time at which, the Doctor facilitated the end of the Last Great Time War. In or with "the Moment", the Doctor destroyed Gallifrey, the invading Dalek forces, the Time Lords, and all the horrific entities created during the Time War. (DW: The End of Time)

The Partisan confirmed to Rassilon and his council that the Doctor was in possession of "the Moment". (DW: The End of Time).

The ninth Doctor once stated that all the combatants of the Time War had burned and been "wiped out in one second". (DW: Dalek) This suggested the literal suddenness of "the Moment".

The modified De-mat Gun, created by the eighth Doctor during the War, might also have been "the Moment", although precise details were unknown. However, the tenth Doctor later referred to the De-mat gun as the device that ended the Time War. (IDW: The Forgotten)