Balefire is a powerful weapon of the One Power, which resembles a thick shaft of intensely bright white light. Anything(except cuendillar)hit with balefire disappears. It burns its target out of the Pattern before its moment of destruction, effectively rolling back anything that the target might have done, except in the memories of those who witnessed it.
Its use has been forbidden since before the Breaking of The World, and was used only sparingly even by Shadowsworn in the War of Power. In that war, sometimes whole cities were destroyed by balefire, and the damage to the Pattern almost unraveled it.