Sorry, I looked it up, and it's spelled Balefire. Wikipedia article:
Here
In the books, balefire was a terrifying weapon, in that firstly, it utterly destroys anything it touches, but more over, it also destroys the soul (so that the person can never be ressurected again).
However, that wasn't the thing balefire is remembered for. The thing balefire is famous for is that it destroys them BEFORE the balefire touches them, with all the paradoxial implications that provides. The stronger the balefire, the further back it removes someone from time, including all the things they've done (people they killed come back to life, that sort of thing).