In
The Wheel of Time, Balefire is a form of
weapon created with
One Power.
Balefire is the most strongest weapon usable with One Power, in a sort. It appears as very bright bar of "liquid fire" when shot. When it hits non-living (doesn't have soul is the definition, I believe) target such as wall or rock, it makes a BF-sized hole, but when it hits living target, it removes the target from the past, cancelling whatever that target had done in between, changing world into what it might have been if the person was gone.
So, A meets B, A kills B, C balefires A so hard it gets cancelled to the beginning => A is dead, B isn't.
<IMO>It is notable that while this definition of BF is functional, actual use of BF in books seems to be incoherent and occasionally self-contradicting and thus couldn't exist.</IMO>
Balefire was rediscovered during War of the Shadow and abused to insane points, completely wiping out complete cities before all sides agreed not to use it (it came close to actually unraveling the Pattern, whatever that means). Its use has been banned ever since, though some Aes Sedai (ie. Moiraine Damodred) seem to think those rules don't apply to them.