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, as his initial method of foiling Rassilon and his plan to bring about the End of Time. (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 Doctor would later state that all the combatants of the Time War had burned, "...wiped out in one second...". (DW: Dalek) This suggests the literal suddenness of "the Moment".

The modified De-mat Gun created by the Doctor may also have been the Moment although precise details are unknown, however the Doctor later referred to the De-mat gun as the device that ended the Time War. (IDW: The Forgotten)